8  "*  SOI  070 


"•  • 


WIRELESS  TELEGRAPHY 

AND 

WIRELESS  TELEPHONY 


AN   UNDERSTANDABLE   PRESENTATION    OF   THE   SCIENCE   OF 
WIRELESS   TRANSMISSION   OF   INTELLIGENCE 


By 

CHARLES    G.   ASHLEY 

ELECTRICAL    ENGINEER 

And 

CHARLES   B.    HAYWARD 

CONSULTING   ENGINEER;   MEMBER,    SOCIETY 
OF   AUTOMOBILE    ENGINEERS 


ILLUSTRATED    ;*\i* 


CHICAGO 

AMERICAN  SCHOOL  OF  CORRESPONDENCE 
1912 


COPYRIGHT  1911  BY 
AMERICAN  SCHOOI,  OF  CORRESPONDENCE 

Entered  at  Stationers'  Hall,  London 
All  Rights  Reserved 


CONTENTS 


The  page  numbers  of  this  volume  will  be  found  at  the  bottom  of  the 
pages;  the  numbers  at  the  top  refer  only  to  the  section. 

WIRELESS   TELEGRAPHY 

Page 

Introduction 1 

Early  forms 2 

Conduction  systems 2 

Induction  systems 4 

Electric  waves 8 

Electromagnetic  theory  of  light 8 

Nature  of  a  wave 11 

Electric  oscillations 12 

Work  of  Hertz .^ 14 

Resonance '. 17 

Wave-lengths 21 

Development  of  radiotelegraphy 23 

The  Righi  oscillator .".  .  24 

The  Branly  coherer 24 

Radiotelegraphy  first  suggested 25 

Work  of  Hughes 27 

Work  of  Lodge. 27 

Work  of  Marconi 27 

Propagation  of  waves  from  a  grounded  oscillator 36 

Selective  signaling 38 

Radiotelegraphic  apparatus 40 

Sources  of  energy 40 

Charging  devices 40 

Induction  coils 41 

Alternating-current  transformers 46 

Oscillation  transformers 47 

Condensers 47 

Tuning  coils 49 

Spark  gaps 49 

High-frequency  alternators 52 

The  singing  arc 53 

Aerials 55 

Directive  antennae 57 

Detectors 57 

Auxiliary  apparatus 66 

Measuring  instruments 67 

Systems  of  radiotelegraphy 68 

Telegraphic  codes 69 

Marconi  system , 69 

Fessenden  system 72 

Telef unken  system 74 

Note. — For  page  numbers  see  foot  of  pages. 

258673 


CONTENTS 

Systems  of  radiotelegraphy  Page 

Von  Lepel  system 76 

Lodge- Muirhead  system 77 

DeForest  system 79 

Clark  system 80 

Stone  system 82 

Massie  system , 83 

Poulsen  system 83 

Other  systems  and  inventors 83 

WIRELESS   TELEPHONY 

Bell's  radiophone 89 

Selenium  cell 90 

Bell's  photophone 91 

"Light  telephony" 91 

Telephony  by  means  of  Hertzian  waves 92 

Nature  of  a  high-frequency  telephone  current 94 

Oscillation  generators 96 

Telephonic  control  of  oscillations 97 

Transmitting  circuits 98 

Receiving  arrangements 102 

Two-way  transmission 104 

Systems  of  radiotelephony 105 

WIRELESS  TELEGRAPHY  IN  AERONAUTICS 

Wireless  on  dirigibles 

Early  experiments  on  balloons 119 

Dangers  from  electric  discharge 120 

Preventive  methods 122 

Wireless  on  the  Zeppelins 124 

Wireless  on  aeroplanes 

First  message 125 

Horton's  experiments 126 

Recent  records 127 

General  problems 130 

Note. — For  page  numbers  see  foot  of  pages. 


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INTRODUCTION 

WIRELESS  TELEGRAPHY  was  the  subject  of  earnest  experi- 
mentation as  early  as  1838,  but  as  far  as  the  public  mind  is  con- 
cerned the  science  began  when  Marconi  sent  his  first  message  across 
the  Atlantic  from  Cornwall  to  Nova  Scotia  in  1902.  This  wonderful 
accomplishment,  like  the  startling  application  of  the  X-raysv  by 
Roentgen,  had  so  much  of  the  spectacular  element  in  it,  that  wireless 
telegraphy  and  Marconi  became  famous  at  once.  The  notable  rescues 
of  the  passengers  of  the  Republic  and  the  Titanic  by  the  aid  of 
wireless  messages  have  only  heightened  this  interest,  and  it  was  to 
satisfy  the  demand  for  a  practical  and  understandable  presentation 
of  the  subject  that  this  little  book  has  been  published. 

C.The  development  of  the  wireless  telegraph  is  carried  out  logic- 
ally from  the  early  forms  to  the  latest  adaptations  of  the  most 
important  systems.  The  discussion  also  includes  its  application 
to  the  aeroplane  and  dirigible. 

CL  Wireless  Telephony,  seemingly  even  more  mysterious  than  teleg- 
raphy, is  being  rapidly  developed,  the  entire  absence  of  the  disturb- 
ing noises,  so  characteristic  of  the  land  telephone,  making  this 
mechanism  especially  attractive.  Its  use  between  ship  and  shore 
for  considerable  distances  has  long  since  passed  the  experimental 
stage. 


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WIRELESS  TELEGRAPHY 

INTRODUCTION 

As  a  first  step  into  the  subject  of  wireless  telegraphy  it  may  be 
well  to  consider  the  meaning  of  the  term.  Wire  telegraphy  is  char- 
acterized by  the  employment  of  extended  metallic  lines  or  conductors 
over  which  it  is  possible  to  transmit  intelligence  electrically  by  means 
of  an  arbitrary  code  of  signals.  Wireless  telegraphy  is  characterized 
by  the  absence  of  such  lines  in  the  accomplishment  of  the  same  end. 
Many  have  confounded  wireless  telegraphy  with  the  system  invented 
by  Marconi;  but  the  latter  is  only  one  form  out  of  many:  the  term 
was  used  to  describe  other  systems  years  before  Marconi's  spec- 
tacular success  added  it  to  the  popular  vocabulary.  As  a  matter 
of  fact  any  system  of  telegraphy  which  successfully  substitutes  some 
other  medium  for  the  connecting  wires,  may  properly  be  called 
" wireless."  The  systems  of  wireless  telegraphy  so  far  proposed  may 
be  classified  as  follows:  Conduction  Systems;  Induction  Systems; 
and  Radiation  Systems. 

The  history  of  the  subject  follows  very  closely  the  above  sequence 
in  point  of  time.  First  came  the  conduction  systems — the  attempt 
to  substitute  the  earth  and  bodies  of  water  in  place  of  the  connect- 
ing lines.  Then  came  the  induction  systems,  taking  advantage  of 
those  peculiar  electrical  phenomena  known  as  electrostatic  and 
electrodynamic  induction:  here  the  substituted  medium  was  the 
ether — that  invisible,  intangible  substance  which  is  supposed  to  fill 
all  space.  Last  came  the  radiation  systems,  which  also  make  use 
of  the  ether,  but  in  a  different  way,  namely,  by  disturbing  it  in  such 
a  manner  as  to  produce  far-reaching  waves  which  can  be  detected 
at  distant  points.  It  is  the  last  type,  known  as  radiotelegraphy, 
which  is  today  paramount,  having  superseded  the  other  two  by 
reason  of  its  superior  utility  and  effectiveness.  Its  startling  develop- 
ment during  the  past  ten  years  may  justly  be  called  a  "fairy  tale  of 
science."  The  earlier  systems  are  important,  however,  as  they 
mark  the  birth  and  the  development  of  an  idea. 


CHAPTER  I 
EARLY  FORMS 

Conduction  Systems.  The  essential  feature  of  all  conduction 
systems  is  that  some  other  form  of  material  conductor  is  substituted 
for  that  of  wires.  These  substitutes  have  been  in  all  cases  either 
earth  or  bodies  of  water,  because  they  are  the  only  natural  conductors 
which  are  sufficiently  common  and  extensive  to  be  utilized. 

Work  of  Steinheil.  Today  it  seems  glaringly  obvious  that  the 
earth  may  be  used  as  a  conductor,  but  in  1838  when  Steinheil,  a 
Bavarian,  accidentally  discovered  this  fact,  it  created  quite  a  sensa- 
tion. He  had  been  experimenting  with  the  steel  rails  of  a  railroad 
trying  to  utilize  them  as  substitutes  for  the  wires  of  a  telegraph  cir- 
cuit, but  was  unable  to  obtain  sufficient  insulation.  He  was  sur- 
prised to  discover,  however,  what  a  high  degree  of  conductivity  the 
earth  possessed,  and  was  led  to  conceive  that  he  might  employ  it 
instead  of  the  return  wire  hitherto  used.  He  made  the  experiment, 
and  with  complete  success,  thus  introducing  into  telegraphy  one  of 
its  most  important  features — the  earth  circuit.  Expanding  the  idea, 
Steinheil  wondered  if  it  were  not  possible  to  telegraph  through  the 
earth  without  using  metallic  conductors  at  all.  This  experiment, 
which  was  successful  over  very  short  distances,  is  said  to  have  been 
the  first  attempt  to  telegraph  without  wires.  Steinheil,  however, 
being  unable  to  signal  farther  than  50  feet,  gave  up  this  method, 
convinced  that  it  was  inexpedient  for  telegraphy. 

Morse  System.  S.  F.  B.  Morse,  who  is  famed  as  the  inventor 
of  wire  telegraphy  and  of  the  code  which  still  bears  his  name,  was, 
by  a  strange  coincidence,  also  one  of  the  pioneers  of  telegraphy 
without  wires.  In  1844  he  addressed  a  letter  to  Congress  in  which 
he  related  his  experiments  in  this  field  and  gave  an  interesting  account 
of  his  inception  of  the  idea.  A  portion  of  the  document,  consider- 
ably abridged,  is  as  follows: 

In  the  autumn  of  1842,  at  the  request  of  the  American  Institute,  I  under- 
took to  give  to  the  public  in  New  York  a  demonstration  of  the  practicability 


EARLY  FORMS  3 

of  my  telegraph,  by  connecting  Governor's  Island  with  Castle  Garden,  a  dis- 
tance of  a  mile;  and  for  this  purpose  I  laid  my  wires  properly  insulated  beneath 
the  water.  I  had  scarcely  begun  to  operate,  and  had  received  but  two  or 
three  characters,  when  my  intentions  were  frustrated  by  the  accidental  de- 
struction of  a  part  of  my  conductors  by  a  vessel  which  drew  them  up  on  her 
anchor  and  cut  them  off.  In  the  moments  of  mortification  I  immediately 
devised  a  plan  for  avoiding  such  accidents  in  the  future,  by  so  arranging  my 
wires  along  the  banks  of  the  river  as  to  cause  the  water  itself  to  conduct  the 
electricity  across.  The  experiment,  however,  was  deferred  until  I  arrived  in 
Washington;  and  on  Dec.  16,  1842,  I  tested  my  arrangement  across  the  canal, 
and  with  success.  The  simple  fact  was  then  ascertained  that  electricity  could 
be  made  to  cross  a  river  without  other  conductors  than  the  water  itself;  but 
it  was  not  until  the  last  autumn  that  I  had  the  leisure  to  make  a  series  of  ex- 
periments to  ascertain  the  law  of  its  passage.  The  diagram,  Fig.  1,  will  serve 
to  explain  the  experiment. 

A,  B,  C,  D,  are  the  banks  of  the  river;  N  P  is  the  battery;  G  is  the  gal- 
vanometer; W  W  are  the  wires  along  the  banks,  connected  with  copper  plates 
/,  g,  h,  i,  which  are  placed  in  the  water.  When  this  arrangement  is  complete, 
the  electricity,  generated  by  the  battery,  passes  from  the  positive  pole  P  to 
the  plate  h,  across  the  river  through  the  water  to  plate  i,  and  thence  around 
the  coil  of  the  galvanometer  to  plate  /,  across  the  river  again  to  plate  g,  and 
thence  to  the  other  pole  of  the  battery  N. 

Morse  here  appends  a  table  of  his  results,  "showing,"  as  he 
says,  "that  electricity  crosses  the  river,  and  in  quantities  in  propor- 


w 


W  P\'\'\'\N 

Fig.  1.    Experiment  of  Morse 

tion  to  the  size  of  the  plates  in  the  water.  The  distance  of  the  plates 
on  the  same  side  of  the  river  from  each  other  also  affects  the  result." 
This  distance  he  states  elsewhere  should  be  three  times  greater  than 
that  from  shore  to  shore  across  the  stream. 

Morse's  plan  contains  in  a  simple  form  all  the  essential  features 
of  all  later  endeavors  to  telegraph  by  the  conduction  method  whether 
utilizing  water  or  earth  as  the  medium.  Lindsay,  Highton,  Bering, 
Stevenson,  Preece,  Smith,  and  others  subsequently  worked  out 
more  elaborate  and  extensive  methods  all  resting  primarily  on  the 


4  WIRELESS  TELEGRAPHY 

same  principle  as  above.  None  of  them  succeeded  in  signaling  much 
farther  than  three  miles.  These  early  results  indicate  the  inherent 
limitations  which  have  ever  remained  as  insurmountable  difficulties 
to  the  commercial  adoption  of  this  form  of  wireless  telegraphy. 

Induction  Systems.  Induction  is  an  electrical  influence  exerted 
by  a  charged  body  or  by  a  magnetic  field  on  neighboring  bodies 
without  apparent  communication.  The  laws  of  it  are  well  known 
to  electrical  science  through  the  classic  researches  of  Faraday.  In- 
duction comprehends  two  classes  of  phenomena  known,  respectively, 
as  electrostatic  induction  and  electrodynamic  induction:  the  former  is 
that  property  of  the  electrostatic  field  which  produces  an  electric 
charge  in  a  conductor  when  brought  into  the  said  field;  while  the 
latter  is  that  property  of  the  magnetic  field  by  virtue  of  which  electro- 
motive forces  are  created  in  conductors  by  a  relative  movement  be- 
tween said  field  and  such  conductors.  Without  attempting  to  go 
further  into  the  matter  here,  it  suffices  to  say  that  investigators  were 
not  slow  in  appreciating  that  induction  offered  a  means  of  communi- 
cation which  could  be  classified  as  " wireless. " 

Dolbear  System.  What  is  now  generally  considered  to  be  an 
extreme  case  of  electrostatic  induction,  is  the  remarkable  system  of 
wireless  communication  invented  by  Prof.  Dolbear  of  Tufts  College, 
Boston,  in  1882.  This  system  is  of  especial  historical  interest  owing 
to  its  startling  resemblance  to  the  system  devised  later  by  Marconi. 
Dolbear's  invention  may  be  best  explained  by  referring  to  Fig.  2. 
The  left  side  represents  the  transmitting  circuit  and  the  right,  the 
receiving  circuit.  B  is  a  battery  connected  through  a  carbon  trans- 
mitter to  the  primary  winding  of  an  induction  coil,  the  secondary 
terminals,  A  and  (7,  of  which  are  connected,  respectively,  with  an 
elevated  wire  and  the  grdund.  The  receiving  end  consists  essen- 
tially of  a  similar  elevated  wire  A  connected  to  one  terminal  of  a 
telephone  receiver,  the  companion  terminal  of  which  is  connected 
directly  with  the  earth.  The  higher  these  wires  are  raised,  the  farther 
signals  can  be  transmitted,  so  that  Dolbear  was  prompted  to  attach 
them  to  kites.  This  is  a  curious  anticipation  of  Marconi's  antennae. 
Dolbear  later  made  many  modifications  in  his  apparatus  in  an  en- 
deavor to  reach  greater  distances  by  employing  condensers  raised  to 
a  considerable  height  and  charged  by  batteries;  but  the  system  re- 
mained in  all  important  respects  the  same  as  shown. 


EARLY  FORMS  5 

The  apparatus  works  as  follows:  The  diaphragm  of  the  tele- 
phone transmitter  is  set  into  vibration  by  talking  or  whistling,  thereby 
producing  variations  of  resistance  in  the  powdered  carbon;  this 
constantly  varies  the  amount  of  current  which  flows  into  the  induc- 
tion coil;  and  consequently  the  wire  A  is  charged  to  potentials  which 
are  constantly  fluctuating  in  value,  the  degree  of  fluctuation  depend- 
ing on  the  degree  of  variation  of  resistance  in  the  transmitter.  The 
wire  A'  at  the  receiving  station  follows  by  electrostatic  induction 
all  the  fluctuations  of  A;  and  with  every  change  of  potential,  currents 
flow  between  A'  and  the  ground  through  the  telephone  receiver  R. 


Fig.  2.     Diagram  of  the  Dolbear  System 

The  latter  consequently  repeats  all  the  vibrations  set  up  in  the  trans- 
mitter, and  the  corresponding  sound  is  reproduced.  This  particular 
method  of  operation  is  telephonic;  but  it  will  be  seen  that  the  same, 
or  rather  better,  results  could  be  obtained  by  a  Morse  key  and  tele- 
phonic receiver. 

Edison  System.  Edison  patented,  in  1885,  a  system  of  inductive 
telegraphy,  the  particular  purpose  of  which  was  to  effect  communi- 
cation with  moving  trains.  The  ordinary  telegraph  wire,  which 
commonly  runs  parallel  to  a  railroad  track,  was  utilized  for  one 
of  the  inductive  circuits,  and  the  train  was  equipped  with  another. 
The  latter  consisted  mainly  of  a  large,  metallic  condensing  plate 
set  on  the  roof  of  the  car  and  connected  to  the  secondary  terminals 
of  an  induction  coil,  to  the  primary  terminals  of  which  were  con- 
nected suitable  transmitting  and  receiving  instruments.  When  the 
Morse  key  in  the  primary  circuit  was  depressed,  the  large  con- 
densing plate  received  static  impulses  and  these  acted  inductively 


6  WIRELESS  TELEGRAPHY 

on  the  neighboring  telegraph  wire,  which  thereby  received  and  con- 
ducted equivalent  impulses  to  the  nearest  station  equipped  with 
proper  receiving  instruments.  Or  in  case  another  train  equipped 
as  above  were  traveling  on  the  same  track,  it  could  pick  off  the 
message  inductively  from  the  telegraph  wire.  In  this  manner  two 
moving  trains  might  communicate.  This  ingenious  system  was  put 
into  practical  operation  on  the  Lehigh  Valley  Railroad  in  1887,  and 
worked  with  undoubted  success;  but  from  a  business  point  of  view 
it  proved  a  failure  as  there  was  no  public  demand  for  such  service. 

Work  ofPreece.  One  of  England's  most  successful  investigators 
in  the  field  of  wireless  telegraphy  was  Sir  Wm.  Preece,  chief  elec- 
trician of  the  British  Postal  Telegraphs.  He  performed  numerous 
experiments  which  added  greatly  to  the  theory  of  all  forms  of  inductive 
and  conductive  communication.  One  of  his  most  successful  achieve- 
ments was  to  effect  inductive  communication  between  Gloucester 
and  Bristol  on  the  banks  of  the  Severn,  a  distance  of  nearly  five  miles. 
Parallel  to  the  two  shores  were  stretched  on  telegraph  poles  two 
closed  wire  circuits  extending  about  14  miles  each.  One  of  these 
circuits  was  traversed  by  a  rapidly  interrupted  current  of  about  .5 
amperes.  A  telephone  receiver  inserted  in  the  companion  circuit 
responded  to  the  frequency  of  the  current  in  the  other  by  a  con- 
tinuous sound  upon  pressure  of  the  transmitting  key.  This  form  of 
communication  was  at  one  time  resorted  to  quite  frequently  between 
stations  separated  by  bodies  of  water  under  which  it  was  inexpedient 
to  lay  cables. 

Such  systems  may  be  characterized  as  "wireless"  only  through 
courtesy,  since  they  demand  an  amount  of  wire  which  far  exceeds 
that  required  by  any  ordinary  wire  system  covering  the  same  dis- 
tance; they  come  under  the  classification  of  wireless  telegraphy, 
however,  since  the  wire  conductors  are  not  continuous,  some  other 
medium  being  interposed. 

In  the  year  1885,  Preece  carried  on  very  extensive  investigations 
upon  the  possibilities  of  induction  as  an  agency  of  communication, 
and  summarized  his  observations  as  follows: 

Although  communication  across  space  has  thus  been  proved  to  be  prac- 
tical in  certain  conditions,  those  conditions  do  not  exist  in  the  cases  of  isolated 
lighthouses  and  light-ships,  cases  which  it  was  specially  desired  to  provide 
for.  The  length  of  the  secondary  must  be  considerable,  and,  for  good  effects, 


EARLY  FORMS  7 

at  least  equal  to  the  distance  separating  the  two  conductors.  Moreover, 
the  apparatus  to  be  used  on  each  circuit  is  cumbrous  and  costly,  and  it  may 
be  more  economical  to  lay  a  submarine  cable. 

These  conclusions  are  equally  true  to  the  present  day.  The 
necessity  for  a  large  base  area  remains  the  prohibiting  factor  in  the 
adoption  of  electromagnetic  induction  systems.  For  a  very  pains- 
taking review  of  the  various  early  attempts  at  this  form  of  telegraphy, 
the  reader  is  referred  to  J.  J.  Fahie's  excellent  book,  "A  History  of 
Wireless  Telegraphy." 

Summary.  The  conduction  and  induction  methods  of  wireless 
telegraphy,  although  of  great  historical  and  experimental  value, 
are  of  little  practical  value.  Today  their  use  is  most  exceptional 
because  their  utility  is  too  limited — the  supreme  test  for  any  system 
of  wireless  telegraphy  being  the  test  of  long  distance.  They  have 
been  superseded  by  a  type  of  wireless  telegraphy  which  can  achieve 
communication  across  an  ocean  if  necessary — a  type  which  is  the 
product  of  an  entirely  different  principle,  the  principle  of  electro- 
magnetic radiation.  In  order  to  differentiate  it  from  other  forms 
of  wireless  telegraphy,  this  system  is  best  denominated  by  the  term 
radiotelegraphy,  and  a  discussion  of  its  underlying  theory,  its 
operation,  and  the  arrangement  of  necessary  apparatus  will  be 
found  in  the  following  chapters. 


CHAPTER  II 
ELECTRIC  WAVES 

Electromagnetic  Theory  of  Light.  In  order  to  understand  ra- 
diotelegraphy  with  any  degree  of  completeness  one  must  first  have 
a  comprehension  of  the  theory  of  electric  waves,  including  the  elec- 
tromagnetic theory  of  light.  This  theory,  with  its  verification,  was 
one  of  the  most  notable  scientific  achievements  of  the  last  century. 
However,  let  it  be  remembered  that,  having  adopted  a  working 
hypothesis — the  most  tenable  one  at  present — to  account  for  the 
ether  and  the  modus  operandi  of  ether  waves,  it  is  necessary  as  well 
as  convenient  to  use  the  terms  and  implications  of  such  hypothesis 
positively  and  with  consistency  throughout.  Such  unqualified  use  of 
terms  might  give  foundation  to  the  charge  of  scientific  dogmatism 
were  it  not  remembered  at  all  times  that  we  are  dealing  with  a 
theory,  generally  accepted,  it  is  true,  but  subject  to  the  trials  and 
mutations  which  such  theories  have  undergone  in  the  past.  The 
reasonings  from  the  working  hypothesis  are  valid  for  the  purpose 
for  which  they  are  here  employed;  but  no  true  scientist  will  at  present 
claim  that  such  reasonings  should  or  can  be  extended  to  the  higher 
realm  of  absolute  truth.  In  the  words  of  H.  Poincare*,  "It  matters 
little  whether  the  ether  really  exists;  that  is  the  affair  of  metaphysicians. 
The  essential  thing  for  us  is  that  everything  happens  as  if  it  existed, 
and  that  this  hypothesis  is  convenient  for  the  explanation  of  the 
phenomena." 

The  electromagnetic  theory  of  light  was  first  completely  stated 
in  1864,  when  James  Clerk  Maxwell,  an  English  mathematician, 
sent  to  the  Royal  Society  a  paper  entitled  "A  Dynamical  Theory  of 
the  Ether,"  wherein  he  demonstrated  his  conviction  that  light  and 
electricity  were  phenomena  of  a  kindred  nature — in  fact,  that  light 
was  an  electrical  manifestation.  Maxwell's  paper  came  as  the  result 
of  a  long  series  of  investigations  which  had  been  carried  on  in  two 
different  departments  of  Physics — Optics  and  Electricity.  These 
investigations  had  led  on  the  one  hand  to  a  theory  of  a  light-bearing 
medium  called  the  luminiferous  ether,  and  on  the  other  hand  to  a 


ELECTRIC  WAVES  9 

» 

theory  of  an  electromagnetic  medium  also  called  the  ether.  Max- 
well made  a  synthesis  of  these  two  theories,  demonstrating  that  the 
hypothetical  medium  was  the  same  in  both  cases,  and  that  it  was 
governed  by  electromagnetic  laws. 

The  Luminiferous  Ether.  When  we  observe  that  light  takes 
time  to  travel  from  place  to  place,  and  that  it  comes  to  the  earth 
from  the  sun  and  stars  across  vast  spaces  which  are  not,  so  far  as 
we  know,  filled  with  tangible  matter,  the  inference  necessarily  fol- 
lows that  light  is  either  a  substance  transmitted  bodily,  like  a  stone 
hurled  from  one  place  to  another,  or  a  physical  state  propagated 
through  a  stationary  medium  in  the  form  of  waves.  Various  inves- 
tigators have  demonstrated  that  light  is  a  phenomenon  of  the  latter 
description — that  it  is  a  physical  state,  or  change  of  state,  propagated 
through  a  stationary  medium  in  the  form  of  undulatory  waves,  the 
velocity  of  the  waves  being  approximately  186,500  miles  per  second. 
Investigators  agreed  to  call  this  medium  the  ether,  prefixing  the  ad- 
jective "luminiferous"  which  means  "light-bearing."  They  had 
neither  seen  nor  felt  the  ether — directly  or  indirectly — but  they 
reasoned  that  the  ether  must  exist,  else  the  facts  of  Optics  were 
inexplicable.  They  held  that  it  must  be  some  peculiar  form  of 
matter  which  interpenetrated  all  ordinary  forms  of  matter,  and 
must  also  be  distributed  everywhere  throughout  the  space  of  the 
universe.  Up  to  Maxwell's  time,  however,  they  knew  almost  nothing 
of  the  ether  itself,  except  that  it  behaved  like  an  incompressible 
liquid,  extremely  tenuous  but  exceedingly  rigid,  and  that  the  waves 
were  of  the  kind  classed  as  "transverse." 

The  Electromagnetic  Medium.  In  the  department  of  Electricity 
a  theory  of  an  electromagnetic  medium  had  also  grown  up,  follow- 
ing on  the  researches  of  Ampere,  Henry,  and  Faraday.  The  fact 
that  electrified  bodies  or  magnets  attracted  or  repelled  each  other 
at  a  distance,  and  that  electric  currents  could  create  other  currents 
in  wires  at  a  distance,  and  that  these  actions  were  not  fundamentally 
dependent  upon  the  presence  of  any  material  substance  in  the  space 
between,  led  these  investigators  to  conceive  that  there  must  be  an 
electromagnetic  medium  by  means  of  which  such  actions  were  trans- 
mitted across  apparently  empty  spaces.  They  named  this  medium 
the  ether,  the  same  name  adopted  by  investigators  in  the  department 
of  Optics;  but  it  was  a  long  time  before  anyone  even  surmised  that 


10  WIRELESS  TELEGRAPHY 

there  was  any  kinship  between  the  luminiferous  medium  and  the 
electromagnetic  medium. 

Work  of  Faraday.  The  first  man  to  hint  at  the  above  possi- 
bility was  Faraday,  who,  in  1845,  discovered  the  singular  fact  that 
the  magnet  exercises  a  peculiar  action  on  light,  the  plane  of  polariza- 
tion of  a  polarized  beam  being  rotated  when  the  beam  passes  along 
a  magnetic  field.  This  seemed  to  show  that  there  was  some  relation 
between  electricity  and  light.  Faraday  persevered  in  these  experi- 
ments. He  wrote  a  paper  entitled  "Thoughts  on  Ray  Vibrations" 
wherein  he  expressed  his  belief  that  radiation  of  all  kinds — light, 
heat,  etc. — were  due  to  a  high  species  of  vibration  of  the  lines  of 
force  in  the  magnetic  field.  Faraday's  speculations  may  be  said  to 
have  been  the  inception  of  the  electromagnetic  theory  of  light;  he 
is  indeed  entitled  to  a  large  share  of  the  credit;  but  his  were  only 
speculations,  unformulated  and  incomplete,  and  it  remained  for 
another  man  to  elaborate  them  into  a  complete  theory  mathematically 
demonstrable. 

Work  of  Maxwell.  When  Maxwell,  in  1864,  sent  his  paper  on 
"A  Dynamical  Theory  of  the  Electromagnetic  Field"  to  the  Royal 
Society,  one  of  his  first  steps  was  to  acknowledge  his  debt  to  Faraday. 
He  writes,  "The  conception  of  the  propagation  of  transverse  magnetic 
disturbances  to  the  exclusion  of  normal  ones  is  distinctly  set  forth 
by  Prof.  Faraday  in  his  'Thoughts  on  Ray  Vibrations.'  The 
electromagnetic  theory  of  light  as  proposed  by  him  is  the  same  in 
substance  as  that  which  I  have  begun  to  develop  in  this  paper,  except 
that  in  1846  there  was  no  data  to  calculate  the  velocity  of  propaga- 
tion." Maxwell  then  proceeds  to  give  new  equations  to  express  the 
relations  between  the  electric  and  the  magnetic  displacements  in 
the  medium  and  the  forces  which  result  from  them.  He  shows  that 
when  magnetic  methods  of  measurement  are  used,  the  unit  of  elec- 
tricity arrived  at  has  a  certain  value;  but  when  purely  electrical 
methods  are  used  the  unit  proves  to  have  a  different  value.  The 
relation  between  these  two  units  is  dependent  on  the  "electric  elas- 
ticity" of  the  medium,  and  when  measured  proves  to  be  a  certain 
velocity — 186,500  miles  per  second.  This  velocity,  in  other  words, 
is  that  velocity  with  which  an  electromagnetic  disturbance  is  propa- 
gated through  the  electromagnetic  field.  It  will  be  remembered 
that  the  velocity  of  light  was  already  known  to  be  about  186,000 


10 


ELECTRIC  WAVES  11 

miles  per  second.  Maxwell  comments  on  the  startling  similarity 
as  follows:  "This  velocity  is  so  nearly  that  of  light,  that  it  seems  we 
have  strong  reason  to  conclude  that  light  itself  (including  radiant 
heat,  and  other  radiations,  if  any)  is  an  electromagnetic  disturbance 
in  the  form  of  waves  propagated  through  the  electromagnetic  field 
according  to  electromagnetic  laws."  In  short,  Maxwell's  theory 
assumes  that  the  entire  material  universe  lies  in  one  all-pervading 
electromagnetic  field,  called  for  convenience  the  ether,  and  if  this 
field  be  disturbed  at  any  point,  the  disturbance  is  propagated  through- 
out the  field  in  the  form  of  waves.  All  those  forms  of  radiant  energy 
which  we  call  light,  heat,  etc.,  are  in  reality  electromagnetic  dis- 
turbances propagated  in  the  form  of  electromagnetic  waves. 

Once  an  electromagnetic  field  is  established,  any  change  which 
alters  the  prevailing  conditions  is  said  to  be  an  electromagnetic  dis- 
turbance. When  a  current  of  electricity  increases  in  strength,  the 
field  around  it  increases  also,  the  lines  of  force  spreading  out  from 
the  conductor  like  ripples  in  a  pond;  but  when  the  current  is  decreased, 
the  lines  of  force  contract,  closing  in  around  the  conductor,  and  the 
energy  of  the  field  shrinks  back  into  the  system.  If  this  process  be 
augmented  so  that  the  periodic  reversals  of  current  produce  oscilla- 
tions of  extremely  high  frequency,  then,  at  each  reversal,  part  of  the 
energy  of  the  lield  radiates  off  into  the  surrounding  medium  as  elec- 
tric waves  and  only  part  of  it  returns  into  the  system.  The  frequency 
with  which  such  periodic  reversals  of  current  take  place  determines 
the  distance  between  the  crests  of  the  waves  radiated  into  space  from 
such  a  system.  Waves  created  in  the  ether  by  this  means  are  called 
electric,  or  Hertzian,  waves,  after  the  German  physicist,  Heinrich 
Hertz.  Before  entering  upon  a  more  detailed  consideration  of  waves 
of  this  character,  the  subject  of  waves  in  general  will  be  considered. 

Nature  of  a  Wave.  When  a  disturbance  is  made  at  any  point 
in  an  elastic  medium,  the  particles  of  the  medium  are  set  into  vibra- 
tion and  the  vibrations  are  passed  on  to  the  neighboring  particles,  so 
that  waves  are  formed ;  and  these  waves  travel  with  a  uniform  velocity 
depending  on  the  nature  of  the  medium,  with  a  result  that  the  dis- 
turbance is  propagated  to  considerable  distances  from  its  point  of 
origin.  There  are  in  general  two  classes  of  waves,  known  as  longi- 
tudinal and  transverse,  the  distinction  between  them  depending  on 
the  direction  in  which  the  particles  vibrate.  When  the  particles 


11 


12  WIRELESS  TELEGRAPHY 

vibrate  along  the  line  in  which  the  disturbance  is  traveling,  the  wave 
is  said  to  be  longitudinal;  when  the  particles  vibrate  at  right  angles 
thereto,  the  wave  is  said  to  be  transverse.  The  general  equation 
for  determining  the  velocity  of  waves  of  either  class  is 

v  =  In 

where  v  stands  for  the  velocity,  /  for  the  wave  length,  and  n  for  the 
frequency,  or  number  of  vibrations  per  second. 

This  equation  holds  equally  true  for  ether  waves  which  mani- 
fest themselves  as  light,  and  for  the  longer  waves  produced  by  high- 
frequency  oscillations  of  an  electric  current,  both  of  which  are  of  the 
transverse  variety.  Indeed  all  forms  of  radiant  energy  are,  accord- 
ing to  the  present  belief,  due  to  ether  waves,  differing  from  one 
another  only  in  length.  As  the  velocity  of  propagation  is  the  same 
for  all — namely,  186,000  miles  per  second — the  frequency  varies 
through  a  wide  range.  Ether  waves  varying  between  certain  definite 
lengths  are  visible  and  produce  the  sensation  of  light;  others  much 
longer  falling  upon  matter  raise  its  temperature,  thus  manifesting 
themselves  as  heat;  still  others,  of  a  wave-length  extremely  small 
even  in  comparison  with  visible  rays,  are  capable  of  penetrating 
matter  as  X-rays;  and  others  again,  of  a  Jength  of  half  a  mile  or  more, 
are  flashed  across  the  Atlantic,  conveying  intelligence  from  the  Old 
World  to  the  New. 

As  there  are  many  methods  of  producing  waves  in  gross  matter, 
so  also  are  there  many  methods  of  producing  waves  in  the  ether. 
The  production  of  electromagnetic  waves  of  a  length  measuring 
from  a  few  inches  to  many  rods  need  only  concern  us  here,  as  it  is 
with  the  production  of  such  waves  that  the  science  of  radiotelegraphy 
deals.  As  before  stated,  a  part  of  the  energy  of  a  very  rapidly  alter- 
nating current  is  radiated  off  into  space  in  the  form  of  electric  waves. 
Under  what  physical  conditions  such  disturbances  are  created  will 
now  be  considered. 

Electric  Oscillations.  If  a  charged  condenser,  or  Leyden  jar, 
is  discharged  through  a  conductor  of  high  resistance,  the  opposing 
polarities  slowly  neutralize  each  other  by  a  current  flowing  in  one 
direction.  If,  however,  the  condenser  is  discharged  through  a  con- 
ductor of  low  resistance,  such  as  a  coil  of  wire  of  a  few  turns,  the 
effect  is  wholly  different.  Under  these  conditions  the  discharge 
consists  of  a  number  of  excessively  rapid  oscillations  of  the  nature 


12 


ELECTRIC  WAVES  13 

of  a  high-frequency  alternating  current,  caused  by  the  self-induction 
of  the  coil,  in  consequence  of  which  the  current  once  set  up  tends  to 
persist.  The  first  rush  of  current  more  than  empties  the  condenser, 
and  charges  it  to  the  opposite  polarity;  then  follows  a  series  of  similar 
discharges  of  diminishing  amplitude  until  the  energy  of  the  charge 
is  entirely  dissipated.  This  process  is  represented  in  Fig.  3. 

The  spark  produced  by  the  discharge  of  a  condenser  under 
these  conditions  appears  to  the  eye  as  a  single  flash,  due  to  the  rapidity 
with  which  the  successive  discharges  follow  one  another.  In  reality 
it  consists  of  several  distinct  sparks  lasting  but  an  exceedingly  small 
fraction  of  a  second. 

The  law  governing  condenser  discharges  is  as  follows:  //  a 
condenser  of  capacity  K  is  discharged  through  a  resistance  R  and 
self-induction  L,  the  result  is  a  unidirectional  discharge  or  a  series 

of  oscillations  according  as  R  is  greater  or  less  than  2-vl  jr* 

A  rapid  oscillatory  discharge  sets  the  electromagnetic  medium 
in  vibration  much  as  a  tuning  fork  sets  the  air  in  vibration  in  pro- 


T/ME  AX/3 


MEGAT/VE 


Fig.  3.     Curve  Representing  an  Oscillatory 
Discharge 


ducing  sound-waves.  Such  discharges  provide  a  simple  means  for 
creating  electric  waves  in  the  ether.  An  understanding  of  condenser 
action  is,  therefore,  of  great  importance  in  a  comprehension  of  the 
principles  of  radiotelegraphy. 

The  oscillatory  nature  of  condenser  discharges  was  known 
when  Maxwell  promulgated  his  electromagnetic  theory,  but  it  was 
not  until  twenty-five  years  after  the  announcement  of  the  theory 
that  scientists  were  able  to  detect  the  presence  of  electric  waves. 
They  knew  the  conditions  under  which  such  waves  should  arise, 


13 


14 


WIRELESS  TELEGRAPHY 


but  none  were  able  to  devise  a  means  to  demonstrate  their  presence. 
It  remained  for  Heinrich  Hertz,  a  pupil  of  the  illustrious  von  Helm- 
holtz,  to  solve  the  mystery  and  give  experimental  verification  to  a 
theory  which  must  ever  remain  one  of  the  greatest  achievements  of 
inductive  reasoning.  Hertz  succeeded  not  only  in  producing  and 
detecting  electric  waves,  but  in  demonstrating  that  such  waves 
possessed  all  the  essential  characteristics  of  light. 

The  Work  of  Hertz.     It  was  in  1888  that  Hertz,  then  thirty 
years  old  and  professor  of  Physics  in  the  University  of  Bonn,  carried 


/MDUCT/OM 
CO/L 

b 

- 

li  •  • 

• 

Fig.  4.     Hertz  Oscillator 

on  the  epoch-making  series  of  experiments  which  have  proven  to 
be  the  foundation  of  the  art  of  radiotelegraphy.  His  apparatus  was 
of  the  simplest  construction.  To  generate  electric  waves  he  em- 
ployed what  is  now  known  as  a  Hertz  oscillator,  Fig.  4.  This  con- 
sists of  two  metallic  conductors  in  the  shape  of  plates  or  spheres, 
each  attached  to  a  small  rod  terminating  in  a  polished  metal  ball. 
These  were  connected  to  the  secondary  terminals  of  an  induction 
coil  and  the  two  balls  brought  into  close  proximity,  thus  forming 
a  small  spark  gap.  It  will  be  seen  that  the  arrangement  has  the 
essential  features  of  a  condenser  whose  plates  are  widely  separated 
and  whose  dielectric  extends  into  the  surrounding  air.  When  the 
charge  is  accumulating  on  the  large  metallic  plates,  a  strong  electric 


ELECTRIC  WAVES  15 

displacement  is  set  up  between  them,  and,  as  the  potential  difference 
rises,  a  point  is  reached  where  the  insulation  of  the  air  gap  breaks 
down  and  a  spark  passes  across  the  gap.  During  the  passage  of  this 
spark  the  air  becomes  highly  conductive  and  the  whole  oscillator 
becomes  one  conductor  for  the  time  being.  The  potential  difference 
between  the  charged  plates  immediately  begins  to  equalize  itself, 
after  the  manner  of  all  oscillatory  condenser  discharges,  by  a  series 
of  rapidly  damped  surges,  and  with  every  oscillation  a  wave  is 
radiated  into  space.  The  waves  emitted  by  a  device  of  this  char- 
acter are  intermittent,  each  complete  discharge  of  the  oscillator 


r 


/v       f  N  p  P  N 

Fig.  5.    Formation  of  Closed  Loops  of  Electric  Strain 

sending  out  a  rapidly  damped  train,  or  group,  of  waves.  The 
frequency  with  which  such  trains  follow  one  another  depends  upon 
the  frequency  of  the  charging  source. 

It  cannot  be  said  that  the  exact  sequence  of  events  in  the  for- 
mation of  an  electric  wave  is  definitely  agreed  upon,  further  than 
that  the  production  consists  in  sending  out  closed  loops  of  force  as 
shown  by  Hertz,  Dr.  F.  Hack,  and  others.  The  subject  is  very 
difficult  to  present  briefly,  but  an  idea  of  the  process  may  be  had  by 
reference  to  Fig.  5. 

The  curved  line  represents  the  form  and  the  direction  of  one 
of  the  many  lines  of  electric  strain  existing  between  the  two  plates 
of  a  Hertz  oscillator.  Every  line  of  electric  strain  according  to  the 
electronic  theory  of  electricity  must  be  a  closed  line  or  loop,  or  else 


15 


16  WIRELESS  TELEGRAPHY 

must  terminate  on  an  electron  and  a  co-electron.  The  figures  A, 
B,  C,  D,  E,  and  F  represent  the  successive  stages  in  the  pro- 
duction of  closed  loops  of  electric  strain.  As  the  charges  oscillate 
to  and  fro  the  lines  of  electrostatic  strain  are  crossed,  making  a  closed 
loop  which  is  immediately  pushed  outward  by  the  following  loop; 
with  the  result  that  the  direction  of  strain  around  each  loop  is  alter- 
nately in  one  direction  and  in  the  other,  as  shown  in  F.  In  addition 
to  these  lines  of  electrostatic  strain  there  are  at  right  angles  to  them 
other  self-closed  lines  of  force  of  a  magnetic  nature,  due  to  the  cur- 
rent passing  during  discharge.  These  magnetic  rings  of  flux  alter- 
nate in  their  direction  at  each  oscillation,  thus  forming  a  series  of 
closed  loops  of  magnetic  flux  co-axial  with  the  oscillator.  Hence 
we  are  called  upon  to  imagine  the  space  around  a  Hertz  oscillator 
as  filled  with  concentric  rings  of  magnetic  flux  periodically  revers- 
ing in  direction  and  having  their  maximum  values  at  instants  when 
the  electrostatic  strains  are  at  their  minimum  values.  These  com- 
plementary modes  of  energy  periodically  varying  in  regard  to  time 
and  space  form  an  electric  wave. 

Energy  of  an  Oscillator.  As  a  portion  of  the  energy  imparted 
to  an  oscillator  in  the  form  of  an  electric  charge  is  expended  in  heat- 
ing the  metallic  balls,  in  creating  a  bright  light,  and  in  producing  a 
noise  at  the  discharge,  it  is  evident  that  the  entire  energy  of  the 
system  is  not  expended  in  the  formation  of  electric  waves.  The 
total  amount  of  energy  which  it  is  possible  to  potentially  store  in 
an  oscillator  in  the  form  of  electrostatic  stress  depends  on  its  elec- 
trical capacity,  and  is  equivalent  to  the  amount  of  energy  which 
could  be  stored  in  a  condenser  of  the  same  capacity.  The  storage 
of  energy  in  a  condenser  is  proportional  to  the  square  of  the  voltage 
to  which  it  is  charged;  which  is  another  way  of  saying  that  a  very 
great  amount  of  energy  could  be  stored  in  a  very  small  condenser 
if  it  were  possible  to  maintain  the  insulation  under  exceedingly  high 
potentials.  The  dielectric  strength  of  the  material  used  for  the 
dielectric  thus  places  a  limit  upon  the  amount  of  energy  it  is  possible 
to  store  in  such  a  device.  A  small  oscillator  could  likewise  have  a 
large  amount  of  energy  imparted  to  it  by  enlarging  the  spark  gap 
enough  to  allow  a  higher  potential  to  be  reached  before  the  insula- 
tion of  the  gap  breaks  down,  were  it  not  for  the  fact  that  the  increased 
resistance  of  the  lengthened  gap  renders  the  spark  non-oscillatory. 


16 


ELECTRIC  WAVES  17 

A  limit  is  therefore  placed  upon  the  potential  which  it  is  practicable 
to  employ  in  the  charging  of  oscillators  or  any  form  of  condenser. 
„  As  the  capacity  of  a  condenser  increases  in  direct  proportion  to  the 
area  of  its  plates — other  factors  remaining  the  same — it  is  evident 
that  the  dimensions  of  an  oscillator  of  the  Hertz  type  determine  the 
amount  of  energy  it  is  possible  to  utilize  in  the  generation  of  electric 
waves. 

Hertz  Resonator.  The  most  important  contribution  of  Hertz 
to  the  subject  of  electric  waves  was  the  discovery  of  a  simple  means 
for  detecting  the  presence  of  such  radiations.  The  fundamental 
character  of  the  discovery  is  apparent  when  it  is  observed  that  the 
device  consists  simply  of  a  single  turn  of  wire  forming  a  ring,  pro- 
vided with  a  spark  gap  between  two  metallic  knobs,  the  distance 
separating  these  terminals  being  adjustable  by  a  screw.  The  de- 
vice, called  a  resonator,  is  shown  in  Fig.  6.  Hertz  discovered  that 
electric  waves  falling  upon  such  a  conductor  were  capable  of  inducing 
therein  alternating  currents  of  the  same 
frequency.  By  holding  his  resonator 
within  a  few  yards  of  an  active  oscillator 
he  found  that  it  became  the  seat  of 
induced  secondary  oscillations  which 
were  strong  enough  to  be  manifested 
by  minute  sparks  visible  between  the 
metallic  balls.  Following  up  this  clue 
he  carried  on  a  very  extensive  series  of 
experiments,  all  tending  to  prove  that 
such  waves  possessed  all  the  character-  Fig  6 

istics   of  light — that   they  were  indeed 

but  "invisible  light."  Hertz'  resonator  may  be  said  to  be  the  first 
"wireless  detector"  known.  The  further  development  of  this  preg- 
nant idea  plays  an  important  part  in  the  evolution  of  the  systems  of 
wireless  telegraphy. 

Resonance.  A  definite  period  of  vibration  is  characteristic 
of  many  things  in  nature,  including  all  sonorous  bodies  such  as 
strings  under  tension,  as  in  the  case  of  the  piano  and  all  stringed 
instruments;  confined  portions  of  air,  as  exemplified  by  the  organ 
pipe ;  and  in  fact  all  bodies  which,  when  displaced  by  the  application 
of  an  external  force,  tend  to  return  by  virtue  of  their  elasticity  and 


17 


18  WIRELESS  TELEGRAPHY 

execute  free  vibrations  until  they  gradually  come  to  rest.  If  very 
feeble  impulses  be  applied  to  a  pendulum  at  rest  at  intervals  exactly 
corresponding  to  its  natural  period  of  vibration,  it  may  be  made  to 
swing  through  an  arc  of  considerable  amplitude.  Bodies  capable 
of  executing  vibrations  by  virtue  of  their  own  resiliency  may  likewise 
be  set  into  powerful  vibration  by  a  series  of  impulses  keeping  time 
with  their  own  natural  period.  Thus  a  tone  from  a  violin  may  draw 
forth  a  responsive  note  from  a  piano,  and  by  the  same  reason  a  piano 
will  often  set  into  sympathetic  vibration  some  fixture  or  article  of 
bric-a-brac.  Also  impulses  communicated  through  the  air  from  a 
sounding  tuning-fork  and  falling  upon  another  of  the  same  pitch, 
will  cause  the  latter  to  hum  a  note  in  unison.  This  phenomenon 
is  called  resonance.  Resonance  is  thus  an  increase,  or  amplifica- 
^  tion,  of  a  periodic  motion  by  an  intermittent  force  of  the  same 
time-period. 

Resonant  effects  are  not  confined  to  the  vibrations  of  gross  matter, 
but  may  also  be  observed  in  connection  with  the  flow  of  electricity 
in  a  circuit.  This  would  seem  to  indicate  that  an  electric  circuit 
possessed  something  analogous  to  a  natural  period  of  vibration — 
which  is  the  case.  This  time-period*  is  due  to  certain  characteris- 
tics of  the  circuit,  namely  capacity,  and  inductance.  The  quantity 
of  electricity  required  to  charge  a  conductor  up  to  unit  potential  or, 
in  other  words,  the  ratio  of  the  charge  on  a  conductor  to  its  poten- 
tial, is  called  capacity.  The  unit  employed  to  measure  capacity 
is  the  farad.  Inductance  is  that  quality  of  an  electric  circuit  by 
virtue  of  which  the  passage  of  an  electric  current  is  necessarily 
accompanied  by  the  absorption  of  energy  in  the  formation  of  a 
magnetic  field.  The  analogy  to  mechanical  inertia  is  very  close, 
and,  for  convenience,  inductance  may  be  thought  of  as  electromag- 
netic inertia  by  reason  of  which  an  electric  current  resists  any  sudden 
change.  The  unit  of  inductance  is  the  henry.  In  all  circuits  pos- 
sessing capacity  and  inductance  there  is  a  storage  of  electrostatic 
energy  due  to  the  potentially  charged  capacity,  and  a  storage  of 
electromagnetic  energy  due  to  the  formation  of  the  magnetic  field 
by  the  current.  Any  electrical  change  taking  place  in  such  a  circuit 
requires  a  readjustment  of  this  stored  energy.  Such  an  adjustment 
takes  place  in  the  form  of  an  oscillatory  current  of  diminishing 
amplitude  until  equilibrium  is  restored.  The  time-period  of  such 


18 


ELECTRIC  WAVES  19 

oscillations    of   energy   is  dependent   upon    the    capacity  and    the 
inductance  of  the  circuit,  and  is  expressed  by  the  equation 


where  L  is  the  inductance  in  henries,  and  K  is  the  capacity  in  farads. 
The  number  of  such  oscillations  per  second,  i.  e.,  the  frequency,  is, 

therefore,  n=  —  .     For  purposes  in  connection  with  wireless  teleg- 

raphy this   equation  is   better    expressed    in    microseconds,   micro- 
henries, and  microfarads. 

The  phenomena  of  electrical  resonance  were  first  illustrated 
by  Sir  Oliver  Lodge  in  his  well-known  experiment  with  his  so-called 
syntonic  jars.  Two  Leyden  jars,  Fig.  7,  are  placed  a  short  distance 
apart.  A  bent  wire  connected  to  the  outer  coating  of  one  serves  as  a 
discharging  circuit  (as  shown)  with  a  short  air,  gap  between  polished 
knobs  at  the  top.  A  circuit  of  wire  whose  inductance  is  rendered 
adjustable  by  a  sliding  cross-piece  —  making  connection  between 
two  conductors—  is  connected  permanently  with  a  second  jar.  This 


Fig.  7.    Lodge  Syntonic  Jars 

jar  is  also  provided  with  a  spark  gap  formed  between  the  outer 
coating  and  a  small  piece  of  tin-foil  extending  from  the  inner  coating 
over  the  lip  of  the  jar  to  within  a  short  distance  of  the  outer  coat- 
ing. By  continually  discharging  the  first  jar  by  connection  with 
an  induction  coil  or  other  suitable  source  of  high  potential,  and  by 
manipulating  the  sliding  cross-plate  in  the  circuit  of  the  other  jar, 
a  point  may  be  found  where  the  latter  will  also  discharge  in  syntony 
with  the  first.  The  two  circuits  are  then  said  to  be  in  tune,  in  syntony, 
or  in  resonance.  When  the  product  of  inductance  by  capacity  is 
the  same  for  two  circuits,  they  have  the  same  natural  period  of 
oscillation. 


19 


20 


WIRELESS  TELEGRAPHY 


Fig.  8.     Closed  Oscil- 
latory Circuit 


As  any  circuit  possessing  inductance  and   capacity   tends   to 
oscillate  electrically  at  its  own  frequency,  it  becomes  the  seat  of  an 
induced  oscillatory  current  when  subjected  to  the  influence  of  elec- 
tric waves  of  that  frequency,  each  wave  giving  a  slight  impulse 
to  the  readily  excited  oscillations,  with  the  result  that  the  induced 
electromotive  forces  will  be  amplified  in  intensity, 
just  as  the  swing  of  a  pendulum  is  amplified  by 
the  application  of  properly  timed,  though  feeble, 
touches.     Circuits  possessing  inductance  and  ca- 
pacity connected   in  series  are  thus  capable  of 
being  "tuned"  to  a  required  frequency  by  a  proper 
adjustment  of  these  two  factors.     Such  circuits 
are  called  oscillatory  circuits  and  may  be  of  many 
forms,   but   can   be   classified  under   two   heads 
known    as   closed    oscillatory    circuits    and   open 
oscillatory  circuits.      Those  circuits  having  their 
capacities   in   the  form  of  condensers   whose    capacity  areas    are 
closely  associated  are  called  "closed,"  and  those  having  their  capacity 
areas  widely  separated  in  such  a  manner  as  to  cause  the  field   of 
electrostatic  stress  to   extend   out  into  the  surrounding  space   are 
called  "open."     In  the  first,  Fig.  8,  the  capacity  is  represented  by 
the  two  metallic  disks  separated  by  a  dielectric  of  air,  and  connected 
by  a  circular  wire  representing  the  inductance  of  one  turn,  while  the 

"open"  type,  Fig.  9,  is  shown  by 
the  two  metallic  capacities  con- 
nected by  a  rod  which  is  cut  in 
two  at  the  center  to  form  a  gap. 
Either  may  or  may  not  have  an 
air  gap  introduced  therein. 

The  similarity  to  the  Hertz  os- 
cillator and  resonator  is  apparent 

at  a  glance.  This  is,  indeed,  more  than  a  similarity,  for  the  Hertz 
oscillator  was  nothing  more  than  an  open  oscillatory  circuit,  and 
his  resonator  a  closed  circuit  of  the  same  variety.  By  separating 
the  plates  of  a  condenser  after  the  manner  of  a  Hertz  radiator,  thereby 
forming  an  open  oscillatory  circuit,  a  large  part  of  the  energy  of  the 
charge  is  radiated  away  in  the  form  of  electric  waves  by  reason  of  the 
dielectric  extending  out  into  the  surrounding  air.  Circuits  of  this 


Fig.  9.     Open  Oscillatory  Circuit 


ELECTRIC  WAVES  21 

type  are,  therefore,  excellent  radiators  but  not  very  persistent  radia- 
tors, because  the  oscillatory  current  is  damped  quickly  by  the 
rapid  dissipation  of  energy  in  the  radiation.  Conversely,  circuits 
of  the  closed  type  are  persistent  vibrators,  but  poor  radiators.  The 
train  of  waves  emitted  by  the  open  type  may  be  compared  to  the  note 
given  forth  from  a  piano  string  when  the  finger  is  immediately  re- 
moved from  the  key  allowing  the  damper  to  rapidly  extinguish  the 
vibration.  The  closed  type  is  comparable  to  a  note  struck  on  the 
same  instrument  but  with  the  damper  raised  by  the  sustaining 
pedal.  As  it  requires  an  increment  of  time  to  start  oscillations  in  a 
tuned  circuit,  it  is  obvious  that  the  closed  type  is  preferable  if  it  can 
be  made  to  radiate  sufficiently.  If  the  damping  of  the  oscillations 
in  a  radiator  takes  place  too  quickly,  the  energy  of  the  charge  will 
be  dissipated  at  the  first  or  second  surge,  in  which  event  the 
exact  timing  of  a  resonating  circuit  is  unimportant.  With  a  persistent 
oscillator,  however,  syntony  between  the  two  circuits  is  of  the  utmost 
importance,  as  otherwise  the  exciting  circuit  will  tend  to  destroy  at 
one  moment  the  oscillations  it  set  up  a  moment  earlier.  Syntony 
is  of  great  practical  value  in  the  application  of  Hertzian  waves  to 
wireless  telegraphy  in  that  it  permits  of  selective  signaling  to  a  cer- 
tain extent  by  the  employment  of  different  wave-lengths,  or  the 
tuning  of  a  receiving  station  to  the  frequency  of  a  sending  station. 
Wave=Lengths.  As  before  mentioned,  the  waves  created  by 
a  Hertz  oscillator  are  of  very  much  lower  frequency  and  are  pro- 
portionally longer  than  light  waves,  but  .their  velocity  is  identical. 
Furthermore,  the  relation  between  the  velocity  of  propagation,  fre- 
quency, and  wave-length  of  ether  waves  was  shown  to  be  expressed 
by  the  equation 

v  =  In 

In  order  to  obtain  numerical  values  for  these  quantities,  it  is  evident 
that  the  value  of  v  must  be  determined  by  reference  to  the  best 
available  experimental  data.  Numerous  investigators  have  agreed 
upon  3  X1010  centimeters  per  second  as  representing  the  most  prob- 
able value  for  this  constant.  Knowing  this,  and  by  assigning  the 
correct  values  to  the  factors  capacity  and  inductance  in  determining 
the  natural  frequency,  it  becomes  a  simple  matter  to  calculate  the 
length  of  wave  emitted  by  a  radiator;  and,  conversely,  by  employ- 
ing the  proper  capacity  and  inductance  a  radiator  may  be  con- 


21 


22  WIRELESS  TELEGRAPHY 

structed  to  give  any  desired  wave-length  within  wide  limits.  Ca- 
pacity and  inductance  may  be  considered  to  be  the  electrical  dimen- 
sions of  an  oscillator,  and  they  determine  the  length  of  wave  emitted, 
just  as  the  note  emitted  from  an  organ  pipe  depends  upon  the  di- 
mensions of  such  a  pipe. 

The  waves  created  by  Hertz  with  various  forms  of  his  oscillator 
varied  between  a  few  inches  and  a  few  feet  in  length.  He  deter- 
mined these  lengths  not  only  by  mathematical  computation  as  ex- 
plained above,  but  by  direct  experimental  test.  He  set  up  at  the 
far  end  of  his  laboratory  a  large  sheet  of  metal  to  reflect  back  the 
waves,  and  then  went  about  the  room  with  his  resonator,  exploring 
the  space  to  find  at  what  points  sparks  were  produced.  He  found 
that  when  waves  are  thus  reflected  back  upon  themselves  there  are 
nodal  points,  just  as  there  are  nodal  points  in  sound-waves  and  in 
light- waves  when  similarly  reflected.  Measuring  the  distances 
between  these  nodal  points  he  was  able  to  determine  the  wave- 
length precisely. 

With  the  simple  instruments  at  his  command  Hertz  carried  on 
many  other  experiments  which  are  little  short  of  beautiful  in  their 
adaptation  of  means  to  ends;  but  we  cannot  go  into  them  here  more 
than  to  say  that  they  all  tended  to  prove  the  main  contentions  of 
Maxwell's  theory.  The  unqualified  success  of  these  experiments 
won  the  admiration  of  scientists  all  over  the  world.  But  few,  if 
any,  realized  at  the  time  that  Hertz,  in  addition  to  giving  indisputable 
proof  to  Maxwell's  famous  hypothesis,  had  also  laid  the  foundations 
for  a  new  and  triumphant  system  of  wireless  telegraphy. 


22 


CHAPTER  III 
THE  DEVELOPMENT  OF  RADIOTELEQRAPHY 

It  is  evident  that  when  Hertz  constructed  an  apparatus  which 
could  transmit  electrical  manifestations  to  a  distance,  without  wires, 
he  possessed  the  elements  of  a  system  of  wireless  telegraphy.  All 
signaling  at  a  distance  whether  by  wire  or  without,  requires  the 
presence  of  three  fundamental  factors:  a  device  to  produce  the 
signal;  a  medium  to  carry  the  signal;  and  a  device  to  receive  the  signal. 
Hertz'  apparatus  with  its  oscillator,  electromagnetic  medium,  and 
resonator,  easily  fulfilled  the  requirements,  and  its  use  as  a  system 
of  wireless  telegraphy  was  merely  a  matter  of  time. 

The  main  line  of  development  was  to  be  an  extension  of  the 
distance  over  which  signals  could  be  transmitted;  for  as  we  have 
seen  in  the  consideration  of  earlier  systems — notably  induction 
systems — distance  is  the  important  factor.  Any  system  which  can- 
not transmit  messages  to  a  considerable  distance  is  of  small  practical 
service  to  the  world.  Hertz  with  his  apparatus  never  succeeded  in 
producing  waves  which  were  detectable  at  more  than  a  score  of  meters 
or  so;  consequently  we  need  not  wonder  that  he  never  suspected  that 
one  of  the  largest  fruits  of  his  achievement  was  to  be  a  system  of 
wireless  trans-oceanic  communication.  When  asked  by  a  civil 
engineer  of  Munich  whether  he  thought  telephonic  communication 
could  be  effected  by  means  of  electric  waves,  he  replied  in  the  negative, 
as  he  considered  that  the  alternations  of  current  in  the  telephone 
were  not  of  a  nature  to  be  detectable.  He  could  not,  of  course,  fore- 
see the  improvements  which  were  destined  to  be  made,  rendering 
his  apparatus  immeasurably  more  sensitive  and  serviceable. 

All  the  scientists  of  Europe  were  stirred  by  the  announcement 
of  Hertz'  discoveries,  and  many  set  about  to  repeat  the  experi- 
men'ts.  With  so  many  minds  bent  upon  a  kindred  purpose  it  is  not 
surprising  to  learn  that  much  new  light  was  thrown  upon  the  sub- 
ject and  many  improvements  made  in  the  form  and  efficiency  of  the 
Hertz  apparatus.  Both  the  radiator  and  the  detector  were  signally 
bettered. 


23 


24 


WIRELESS  TELEGRAPHY 


The  Righi  Oscillator.  One  of  the  disadvantages  of  Hertz* 
radiator  lay  in  the  fact  that  the  sparks  in  a  short  time  oxidized  the 
little  knobs  and  roughened  their  surfaces,  resulting  in  irregular 
action.  Prof.  Righi  of  Bologna  overcame  this  difficulty  by  partly 
enclosing  two  metal  spheres,  A  and  B  in  Fig.  10,  in  an  oil-tight 
case  so  that  the  outside  hemispheres  of  each  are  exposed,  the  inner 
hemispheres  being  immersed  in  vaseline  oil  with  only  a  minute  gap 
between  them.  In  a  line  with  these  spheres  are  ranged  two  smaller 
spheres,  C  and  D,  which  form  the  secondary  terminals  of  the  induc- 
tion coil.  Thus  three  sparks  are  produced:  one  between  C  and  A, 
another  between  A  and  J5,  and  another  between  B  and  D.  It  is 
between  A  and  B  in  the  oil  gap  that  the  oscillatory  spark  takes  place, 
the  other  two  sparks  serving  merely  to  charge  the  large  spheres. 
This  arrangement  not  only  produced  a  more  constant  spark  by 
preventing  the  pitting  of  the  electrodes  but  greatly  extended  the 
range  of  wave-lengths  which  it  was  possible  to  employ  in  investi- 
gations of  this  character.  The 
dimensions  of  the  oscillator  could 
thereby  be  reduced  and  the  am- 
plitude of  the  oscillations  greatly 
increased  by  reason  of  the  fact 
that  higher  potentials  could  be 
reached  before  the  energy  was 
released  by  discharge.  Righi 
obtained  oscillations  of  a  fre- 
quency of  12,000,000,000  vibra- 
tions per  second  by  the  use  of 
small  spheres  A  and  B  eight 

Fig.  10.     Righi  Oscillator  .ir  .       ,. 

millimeters  in  diameter. 

The  Branly  Coherer.  The  next  important  advance  pertained 
to  an  improvement  over  the  Hertz  resonator  as  a  means  of  detecting 
electric  waves.  It  was  based  on  the  discovery  of  M.  E.  Branly  and 
others,  that  the  enormous  resistance  offered  to  the  passage  of  an 
electric  current  by  powders  and  metal  filings  is  greatly  reduced  under 
the  influence  of  electric  oscillations.  The  resistance  of  such  con- 
ductors may  drop  instantly  from  thousands  of  ohms  to  hundreds 
by  the  action  of  induced  oscillations,  retaining  this  conductivity 
until  "decohered"  by  a  mechanical  blow.  It  will  be  readily  seen 


24 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY   25 

that  this  provides  a  simple  means  of  effecting  the  operation  of  a 
translating  device  by  acting  as  a  valve  in  turning  on,  as  it  were,  a 
greater  current  in  a  local  battery  circuit.     By  utilizing  this  property 
of    increased     conductivity    Sir 
Oliver  Lodge  succeeded  in  caus- 
ing   the    deflection   of  a    galva- 
nometer.   The  device  employed 
by    Lodge    consisted  of  a  glass 
tube  in  the  ends  of  which  were 
sealed  terminal  wires   connected  Fig  n     Lodge  Coherer 

to    metallic     electrodes    of    the 

same  diameter  as  the  tube,  and  between  the  electrodes  was  placed  a 
small  quantity  of  iron  filings,  as  shown  in  Fig.  11.  This  device  is 
known  as  a  coherer,  a  name  suggested  by  Lodge.  In  various 
modified  forms  the  instrument  has  been  employed  up  to  the  present 
day  in  different  wireless  systems.  Its  practical  application  will  be 
fully  considered  later  in  connection  with  the  work  of  Marconi. 

Radiotelegraphy  First  Suggested.  As  the  Righi  oscillator  and 
Branly  coherer  were  immeasurably  more  efficient  than  Hertz*  cor- 
responding apparatus,  it  necessarily  follows  that  waves  could  be 
sent  and  detected  over  much  longer  distances  and  the  time  was 
getting  ripe  for  the  application  of  these  devices  to  the  purposes  of 
wireless  telegraphy.  The  first  man  to  suggest  this  possibility  is 
said  to  have  been  Sir  Wm.  Crookes,  the  eminent  English  chemist 
and  physicist.  In  a  magazine  article  which  appeared  in  1892  he 
made  the  following  marvelous  forecast  of  Radiotelegraphy: 

Rays  of  light  will  not  pierce  through  a  wall,  nor,  as  we  know  only  too 
well,  through  a  London  fog;  but  electrical  vibrations  of  a  yard  or  more  in 
wave-length  will  easily  pierce  such  media,  which  to  them  will  be  transparent. 
Here  is  revealed  the  bewildering  possibility  of  telegraphy  without  wires,  posts, 
cables,  or  any  of  our  costly  appliances.  Granted  a  few  reasonable  postulates, 
the  whole  thing  comes  well  within  the  realms  of  possible  fulfillment.  At 
present  experimentalists  are  able  to  generate  electric  waves  of  any  desired 
length,  and  to  keep  up  a  succession  of  such  waves  radiating  into  space  in  all 
directions.  It  is  possible,  too,  with  some  of  these  rays,  if  not  with  all,  to 
refract  them  through  suitably  shaped  bodies  acting  as  lenses,  and  so  to  direct 
a  sheaf  of  rays  in  a  given  direction.  Also  an  experimentalist  at  a  distance  can 
receive  some,  if  not  all,  of  these  rays  on  a  proper  instrument,  and  by  concerted 
signals,  messages  in  the  Morse  code  can  pass  from  one  operator  to  another. 

What  remains  to  be  discovered  is — firstly,  simpler  and  more  certain 
means  of  generating  electrical  rays  of  any  desired  wave-length,  from  the 


26  WIRELESS  TELEGRAPHY 

shortest,  say  a  few  feet,  which  will  easily  pass  through  buildings  and  fogs,  to 
those  long  waves  whose  lengths  are  measured  by  tens,  hundreds,  and  thou- 
sands of  miles;  secondly,  more  delicate  receivers  which  will  respond  to  wave- 
lengths between  certain  defined  limits  and  be  silent  to  all  others;  and  thirdly, 
means  of  darting  the  sheaf  of  rays  in  any  desired  direction,  whether  by  lenses 
or  reflectors,  by  the  help  of  which  the  sensitiveness  of  the  receiver  (apparently 
the  most  difficult  of  the  problems  to  be  solved)  would  not  need  to  be  so  delicate 
as  when  the  rays  to  be  picked  up  are  simply  radiating  into  space,  and  fading 
away  according  to  the  law  of  inverse  squares.  .  .  * 

At  first  sight  an  objection  to  this  plan  would  be  its  want  of  secrecy. 
Assuming  that  the  correspondents  were  a  mile  apart,  the  transmitter  would 
send  the  waves  out  in  all  directions,  and  it  would,  therefore,  be  possible  for 
anyone  living  within  a  mile  of  the  sender  to  receive  the  communication.  This 
could  be  got  over  in  two  ways.  If  the  exact  position  of  both  sending  and 
receiving  instruments  were  known,  the  rays  could  be  concentrated  with  more 
or  less  exactness  on  the  receiver.  If,  however,  the  sender  and  receiver  were 
moving  about,  so  that  the  lens  device  could  not  be  adopted,  the  correspondents 
must  attune  their  instruments  to  a  definite  wave-length,  say,  for  example, 
50  yards.  I  assume  here  that  the  progress  of  discovery  would  give  instru- 
ments capable  of  adjustment  by  turning  a  screw,  or  alternating  the  length  of 
a  wire,  so  as  to  become  receptive  of  waves  of  any  preconcerted  length.  Thus, 
when  adjusted  to  50-yard  waves,  the  transmitter  might  emit,  and  the  receiver 
respond  to,  rays  varying  between  45  and  55  yards,  and  be  silent  to  all  others. 
Considering  that  there  would  be  the  whole  range  of  waves  to  choose  from, 
varying  from  a  few  feet  to  several  thousand  miles,  there  would  be  sufficient 
secrecy,  for  the  most  inveterate  curiosity  would  surely  recoil  from  the  task 
of  passing  in  review  all  the  millions  of  possible  wave-lengths,  on  the  remote 
chance  of  ultimately  hitting  on  the  particular  wave-length  employed  by  those 
whose  correspondence  it  was  wished  to  tap.  By  coding  the  message  even 
this  remote  chance  of  surreptitious  tapping  could  be  rendered  useless. 

This  is  no  mere  dream  of  a  visionary  philosopher.  All  the  requisites 
needed  to  bring  it  within  the  grasp  of  daily  life  are  well  within  the  possibilities 
of  discovery,  and  are  so  reasonable  and  so  clearly  in  the  path  of  researches 
which  are  now  being  actively  prosecuted  in  every  capital  of  Europe,  that  we 
may  any  day  expect  to  hear  that  they  have  emerged  from  the  realms  of  specu- 
lation into  those  of  sober  fact."  .  .  . 

The  purposes  and  problems  of  radiotelegraphy  are  admirably 
stated  in  the  above.  Some  of  those  problems  have  not  even  yet 
been  solved,  as  we  shall  see.  When  Crookes  wrote,  the  idea  of 
radiotelegraphy  was  in  the  air,  and  many  men  indeed  were  striving 
to  turn  the  possibility  into  a  reality.  Several  Englishmen  almost 
achieved  the  desired  end,  but,  strangely  enough,  faltered  or  failed 
when  success  was  within  easy  reach.  Among  these,  mention  must  be 
made  of  Prof.  D.  E.  Hughes,  who,  but  for  a  combination  of  bad 
luck  and  human  fallibility,  might  have  been  today  the  accredited 
discoverer  not  only  of  radiotelegraphy  but  of  electric  waves  as  well. 


26 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY         27 

Work  of  Hughes.  As  far  back  as  1879,  when  experimenting 
with  his  celebrated  microphone  (which  is  in  reality  nothing  other 
than  a  Branly  coherer  reduced  to  its  simplest  elements)  Hughes 
observed  peculiar  electrical  effects  operating  at  a  distance,  and  he 
concluded  that  they  were  due  to  invisible  electric  waves.  He  did 
not,  however,  so  far  as  we  know,  relate  these  phenomena  with  the 
theories  of  Maxwell,  as  Hertz  did,  and  was  consequently  at  a  loss 
to  fully  account  for  them.  He  investigated  the  subject  for  several 
years  and  actually  succeeded  in  telephoning  wirelessly  over  consider- 
able distances.  These  experiments  were  repeated  before  Prof.  Stokes, 
the  president  of  the  Royal  Society,  and  Prof.  Huxley;  but  these 
gentlemen  expressed  doubts  as  to  the  nature  of  the  phenomena, 
with  the  result  that  Hughes  became  infected  with  their  scepticism 
and  abandoned  his  efforts,  believing  himself  on  the  wrong  track.  If 
he  had  persisted  in  his  researches  he  might  have  gathered  the  laurels 
that  later  went  to  Hertz  and  Marconi.  It  has  been  said  that  "Hughes' 
experiments  of  1879  were  virtually  a  discovery  of  Hertzian  waves 
before  Hertz,  of  the  coherer  before  Branly,  and  of  wireless  telegraphy 
before  Marconi  and  others,"  and  the  truth  of  the  statement  must 
be  admitted  to  some  extent. 

Work  of  Lodge.  Mention  must  be  made  of  the  great  debt  which 
radiotelegraphy  owes  to  Sir  Oliver  Lodge  for  his  many  valuable 
contributions  both  to  practice  and  theory.  He  has  been  in  the  fore- 
front of  every  advance  made  in  the  science  of  radiotelegraphy,  and 
might  in  all  truth  be  called  its  patron  saint.  To  him  is  due  our 
knowledge  of  the  principles  of  syntony  which  forms  such  a  vital 
part  of  all  modern  systems.  He  was  the  first  man  to  employ  the 
Branly  coherer  as  a  detector  of  Hertzian  waves,  and  while  engaged 
in  demonstrating  the  discoveries  of  Hertz  was  sending  signals  over 
distances  measurable  in  hundreds  of  feet.  That  such  signals  could 
be  utilized  to  convey  intelligence  by  the  simple  application  of  the 
Morse  telegraphic  code  did  not  occur  to  him;  if  he  had  realized  this 
possibility  he  might  have  antedated  Marconi's  invention  of  wireless 
telegraphy. 

Work  of  Marconi.  Passing  over  Popoff,  Rutherford,  Jackson, 
Minchin,  and  others,  several  of  whom  did  important  and  original 
work,  we  come  to  Marconi  who,  in  the  popular  mind,  is  credited 
with  the  whole  achievement  of  radiotelegraphy.  It  is  true  that 


27 


28 


WIRELESS  TELEGRAPHY 


Marconi  carried  radiotelegraphy  through  to  practical  success;  or, 
as  A.  T.  Story  puts  it,  "he  carried  forward  into  the  domain  of 
practical  reality  what  had  only  floated  indistinctly  before  the  minds 
of  others,  or  had  served  them  for  modest  experiments."  But  as 
regards  those  vital  arid  fundamental  developments  of  theory  and 
practice  without  which  radiotelegraphy  would  still  be  a  thing  un- 
known, Marconi  is  only  an  able  follower  and  not  one  of  the  pioneers. 
The  history  of  radiotelegraphy  might  be  shortly  indicated  by  the 
following  list  of  names:  Faraday,  Maxwell,  Hertz,  Righi,  Lodge, 
Marconi.  The  theory  of  electric  waves  originating  with  Faraday 
and  expanded  by  Maxwell,  was  experimentally  demonstrated  by 
Hertz.  Then  came  Righi  and  Lodge  with  their  improvements  on 

the  Hertz  apparatus,  greatly  ex- 
tending its  sphere  of  utility;  and 
finally  Marconi,  who  brought  to- 
gether the  results  achieved  by  his 
predecessors  and,  adding  some- 
thing of  his  own — "a  far-seeing 
initiative  where  others  had  not 
gone  beyond  timid  projects  or 
tentative  research" — produced  a 
successful  system  of  wireless  teleg- 
raphy. Marconi,  who  is  an 
Italian  by  birth,  first  became 
interested  in  Hertzian  waves  when 
a  student  under  Prof.  Righi  at 

the  Bologna  University.  He  was  not  long  in  seeing  their  possible 
application  to  telegraphy,  and  made  some  experiments  with  that 
purpose  in  view.  Becoming  convinced  of  the  feasibility  of  the 
project,  but  finding  no  one  in  Italy  ready  to  take  it  up,  he  set 
out  for  England  to  try  his  fortune.  Arriving  there,  he  applied 
to  the  Patent  Office  for  protection  on  his  ideas,  and  then  took 
the  proposition  to  Sir  Wm.  Preece,  chief  of  the  British  Postal 
Telegraphs.  Preece  gave  Marconi  ready  encouragement,  and  he 
was  soon  conducting  experiments  under  the  auspices  of  the  British 
Post  Office. 

Early  Apparatus.    The  early  apparatus  of  Marconi  consisted  es- 
sentially of  a  Righi  oscillator  and  Branly  coherer,  disposed  in  suitable 


Fig.  12.     Early  Marconi  Transmitter 
Circuit 


28 


THE  DEVELOPMENT  OF  RADIOTELEGKAPHY    29 

circuits  for  generating  and  recording  the  flow  of  waves.  The  trans- 
mitting arrangement  consisted  of  an  induction  coil  producing  the 
requisite  high  potential  with  which  to  charge  a  Righi  oscillator, 
and  a  Morse  key  of  heavy  construction  with  which  to  break  the 
primary  circuit  of  the  coil,  connected  with  a  battery  of  about  five 
cells.  The  actual  transmission  of  messages  was  effected  by  the 
intermittent  movement  of  the  Morse  key  which,  upon  completing 
the  circuit,  started  the  interrupter  of  the  coil  which  remained  in 


Fig.  13.     Early  Marconi  Receiving  Circuit 

operation  as  long  as  the  key  was  held  down;  thus  the  duration  of 
waves  from  the  oscillator  was  made  dependent  on  the  position  of 
the  key.  It  was  thus  possible  by  the  proper  manipulation  of  the 
key  to  send  a  series  of  long  or  short  wave  trains  corresponding  to  the 
dots  and  dashes  of  the  Morse  alphabet.  Fig.  12  represents  dia- 
grammatically  these  features  of  the  sending  station. 

The  receiving  apparatus,  indicated  in  Fig.  13,  consisted  prin- 
cipally of  the  Branly  coherer  somewhat  modified  in  construction 
and  associated  with  suitable  auxiliary  apparatus  for  recording  the 
duration  of  the  received  wave  trains  in  the  form  of  dots  and  dashes 


29 


30 


WIRELESS  TELEGRAPHY 


upon  a  moving  paper  surface  after  the  manner  of  the  Morse  recorder, 
well  known  in  wire  telegraphy.  As  the  coherer  retains  its  low  con- 
ductivity even  after  the  cessation  of  a  train  of  waves,  it  becomes 
necessary  to  provide  means  for  automatically  imparting  a  slight 
blow  or  jar  to  the  tube  in  order  to  restore  its  receptiveness  after 
each  and  every  signal.  Such  a  device  was  used  by  Lodge  and  is 
known  as  a  "tapper."  It  is  generally  in  the  form  of  an  electric 
trembling  mechanism,  such  as  an  electric  bell,  operated  by  a  local 
battery  when  thrown  into  the  circuit  by  a  Morse  relay — the  latter 
acting  in  response  to  the  increase  of  current  when  the  coherer  acts. 
The  coherer  used  by  Marconi  at  this  time  was  his  own  special 
modification  of  the  Branly-Lodge  type.  It  consisted  of  a  glass  tube 


Fig.  14.    Marconi  "Capacity  Areas" 

about  4  centimeters  long  and  2.5  millimeters  in  diameter,  into  which 
were  tightly  fitted  two  silver  terminals  separated  to  a  distance  of  one 
millimeter,  this  space  being  filled  with  a  powdered  mixture  of  96 
parts  nickel  to  4  parts  silver,  worked  up  with  a  trace  of  mercury. 
The  tube  was  exhausted  of  air  and  hermetically  sealed.  To  the 
terminals  of  this  coherer  were  connected  two  resonance  plates,  or 
strips  of  copper,  whose  dimensions  were  such  as  to  bring  the  system 
into  resonance  with  the  oscillator.  Also  connected  to  the  terminals 
of  the  coherer  were  two  choke  coils,  whose  function  was  to  confine 
the  oscillations  to  the  coherer;  and  a  Morse  relay  in  series  with  a 
battery  of  one  cell.  Fig.  13  plainly  shows  the  arrangement. 


30 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY    31 

In  addition  to  the  above  a  tapper  was  provided  to  decohere 
the  metal  filings,  and  also  a  signal  recorder.  The  tapper  was  in 
the  form  of  a  small  electric-bell  mechanism  whose  clapper  con- 
tinuously tapped  the  glass  tube  as  long  as  the  Morse  relay  com- 
pleted the  circuit  in  which  the  tapper  was  placed.  The  Morse  relay 
thus  acts  as  a  switch  by  means  of  which  the  signal  recorder  and 
tapper  are  operated  simultaneously.  It  might  be  well  to  state  that 
the  coherer  holds  its  conductivity  during  the  passage  of  the  oscilla- 
tions even  though  in  vibration  from  the  tapper. 

Capacity  Areas.  A  very  significant  step  taken  by  Marconi  at 
this  early  period  was  his  employment  of  "capacity  areas"  in  the 
circuit  of  his  oscillator,  Fig.  14. 
The  essential  features  of  this  in- 
novation were  as  follows :  T  and 
T  are  metal  plates  joined  to  the 
balls  of  the  oscillator;  C  is  the 
induction  coil.  The  object  of 
this  arrangement  was  to  give 
greater  energy  to  the  oscilla- 
tions, the  carrying  power  of  the 
apparatus  being  found  to  in- 
crease with  the  size  of  the  capac- 
ity areas,  and  with  the  distance 
of  the  same  from  each  other. 
Two  similar  plates  were  also 
attached  to  the  coherer  at  the 
receiving  station.  Though  this 
arrangement  of  capacity  areas 
was  soon  abandoned,  it  marks, 
nevertheless,  the  inception  of  an 
idea  which  developed,  as  we 
shall  see,  into  one  of  the  most 
important  features  of  modern  aerial  telegraphy,  namely,  the  antenna. 

Development  of  the  Antennae.  Endeavoring  to  increase  the 
effectiveness  of  his  capacity  areas  by  enlarging  them  and  separating 
them  as  much  as  possible,  Marconi  conceived  the  idea  of  utilizing 
the  earth  for  one  of  the  plates,  and  of  raising  the  remaining  plate  to 
a  considerable  height  in  order  to  increase  the  distance  between  them. 


Fig.  15.     Diagram  Showing  the 
Earthed  Oscillator 


81 


32 


WIRELESS  TELEGRAPHY 


&4PAC/TY 
AREA 


The  arrangement,  Fig.  15,  then  took  on  the  following  aspect:  coil 
and  oscillator  are  of  standard  type;  E  is  the  earth  connection; 
and  W  the  elevated  plate.  The  higher  the  capacity  area  W  is 
situated,  the  greater  the  distance  to  which  communication  can  be 
carried;  so  it  will  be  seen  that  the  capacity  area  might  with  great 
advantage  be  attached  to  a  kite,  or  captive  balloon.  The  latter 
were,  indeed,  employed  by  Marconi  and  with  very  good  effect. 

Corresponding  changes  were  made 
at  the  receiving  station  also,  by 
employing  a  similar  arrangement 
of  capacity  area,  shown  in  Fig.  16. 
Later  Marconi  became  con- 
vinced that  the  effectiveness  of 
his  aerial  line  was  due  not  to  the 
capacity  at  the  end  of  the  wire, 
but  to  the  length  of  the  wire  itself; 
consequently  he  abandoned  the 
capacity  area  altogether  and  held 
simply  to  the  form  of  vertical 
wires  attached  to  poles  or  kites, 
or  even  to  high  buildings  or 
towers.  These  were  called  an- 
tennae, or  aerials.  The  antenna 
consisting  of  a  single  wire  later 
developed  into  the  multiple  an- 
tenna of  several  wires,  each  ad- 
ditional wire  adding  to  the  capac- 
ity of  the  system.  The  antennae 

of  many  large  stations  are  formidable  structures  of  great  complexity, 
as  the  picture  of  the  South  Wellfleet  station,  Fig.  17,  will  indicate. 
Inductive  Receiving  Antennae.  Another  of  Marconi's  early 
and  important  modifications  was  the  introduction  of  inductive  an- 
tennae into  the  receiver  arrangement.  The  antenna  was  cut  out  of 
direct  conductive  connection  with  the  coherer  circuit  and  allowed  to 
act  on  the  latter  only  by  induction  through  the  agency  of  an  oscilla- 
tion transformer  called  in  common  parlance  a  jigger,  the  theory  of 
which  cannot  be  fully  discussed  here.  Mention  will  be  made,  how- 
ever, of  the  fact  that  such  a  transformer  properly  designed  in  regard 


EARTH 
Fig.   16.    Earthed  Receiving  Circuit 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY   33 

to  the  wave-length  used  not  only  steps  up  the  voltage  so  as  to  increase 
its  effect  on  the  coherer,  but  also  enables  the  coherer  to  be  placed  at 
a  nodal  point  of  the  secondary  oscillations.  As  this  form  of  detector 


Fig.  17.     South  Wellfleet  Wireless  Station 

is  of  the  potentially  operated  variety,  the  practical  importance  of 
the  modification  is  apparent.  A  coherer  placed  in  series  between 
the  antennae  and  ground,  as  in  former  arrangements,  is  poorly  located, 
as  at  the  base  of  an  aerial  the  potential  is  a  minimum  and  the  current 
a  maximum.  Marconi  increased  the  distance  over  which  it  was 
possible  to  signal  nearly  ten  times  by  the  employment  of  this  simple 


SECONDARY* 


AX/S 


_  GLASS  .TUBE  __ 


Fig.  18.     Diagram  of  Oscillation  Transformer  Winding 


device.  His  patents  on  this  improvement  bear  the  dates  of  1898 
and  1899.  Fig.  18  shows  a  diagrammatic  cross-section  of  the  jigger, 
the  zigzag  lines  representing  the  successive  layers  of  the  windings 
wound  in  such  a  manner  that  the  inner  layers  have  the  greatest  num- 


33 


34 


WIRELESS  TELEGRAPHY 


ber  of  turns,  the  primary  having  about  100  and  the  secondary  about 
1,000  turns.  Fig.  19  shows  the  receiver-circuit  with  the  jigger  em- 
bodied therein.  It  will  be  noticed  that  the  local-battery  circuits  are 
the  same  as  used  before,  but  the  jigger  necessitates  a  slight  modifica- 
tion in  the  location  of  the  coherer.  A  condenser  is  connected  to  the 
inner  terminals  of  the  secondary,  the  outer  terminals  of  which  are 
connected  to  the  coherer.  The  local  battery  circuit  is  also  con- 
nected to  the  inner  ends  of  the  secondary  and  across  the  condenser. 
Inductive  Transmitting  Antennae.  It  has  already  been  shown 
that  the  early  capacity  areas  had  given  place  to  the  extended  wire 
raised  to  a  great  height;  and  it  soon  became  evident  that  transmission 

could  be  further  facilitated  by 
devising  a  more  persistent  oscil- 
lator than  that  which  was  em- 
ployed with  the  directly  connected 
aerial.  It  was  possible  to  store 
a  fair  amount  of  energy  in  the 
old  type  of  aerial,  but  the  direct 
connection  entailed  the  disadvan- 
tage 0f  permitting  the  apparatus 
to  radiate  its  entire  amount  of 
energy  almost  instantly  instead 
of  radiating  such  energy  in  the 
form  of  "a  more  continuous  train. 
This  was  not  a  quality  tending  to 
make  for  a  clearly  defined  reso- 
nance between  the  sending  and 
receiving  circuits,  and  means  were 
sought  to  accomplish  a  more  per- 
sistent, or  less  damped,  series  of  oscillations.  The  early  form  of  open- 
circuit  oscillator,  therefore,  gave  place  to  what  is  known  as  the  Marconi- 
Braun  type  of  closed  oscillating  circuit  which,  while  not  so  powerful  a 
radiator,  was  a  very  much  more  persistent  one.  The  method  was  due 
to  Prof.  Braun,  but  in  a  ^modified  form  was  first  used  by  Marconi. 
The  diagram  of  Fig.  20  makes  clear  the  fundamental  idea,  an  idea 
which  has  proven  to  be- of  great  value.  Though  modified  in  number- 
less ways  by  subsequent  inventors,  the  broad  idea  of  associating  the 
aerial  with  a  closed  oscillating  circuit  has  become  almost  universal. 


vwwvwv 

SECONDARY 


Fig.  19.     Marconi  Receiver-Circuit  with 
Jigger 


34 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY 


35 


CONDENSE* 


The  transformer  used  for  this  purpose  is  very  different  from 
the  ordinary  induction  coil  or  alternating-current  transformer  em- 
ployed in  connection  with  low  voltages  and  low  frequencies.  It  will 
be  fully  described  later  under  the  head  of  oscillation  transformers; 
for  the  present  it  is  sufficient  to  say  that  it  forms  an  inductive  couple 
between  the  two  oscillatory  circuits,  the  closed  circuit  being  but  a 
means  of  charging  the  open  circuit  of  the  antennae.  The  antennae 
circuit,  having  a  certain  amount 

of   capacity  and  inductance  de-  AER/AL 

pending  on  its  design  and  posi- 
tion, possesses  a  natural  time- 
period  of  its  own;  so  in  order  to 
induce  in  such  a  circuit  oscilla- 
tions of  a  maximum  amplitude, 
the  primary  circuit  associated 
therewith  must  have  the  same 
natural  time-period.  In  other 
words,  resonance  must  be  estab- 
lished; two  circuits,  as  before 
mentioned,  being  in  resonance 
when  the  product  of  capacity  and 
inductance  is  the  same  for  both. 
The  Marconi-Braun  method  of 
charging  the  aerial  permits  of  the 
employment  of  very  large  capaci- 
ties, with  proportionally  larger 
energy-storing  ability  and  smaller  Fis  20 
inductances  in  the  primary  circuit, 
so  that  the  product  of  these  two  factors  can  be  made  to  equal  the 
product  of  the  corresponding  factors  in  the  antenna  circuit.  The 
efficiency  of  the  transformer  thus  very  largely  depends  on  the  estab- 
lishment of  syntony  between  the  closed  oscillatory  circuit  forming  the 
primary  and  the  open  oscillatory  circuit  forming  the  secondary. 

Another  method  of  associating  the  radiating  aerial  with  a  closed 
oscillatory  circuit,  possessing  many  of  the  advantages  of  the  Marconi- 
Braun  inductive  couple,  is  shown  in  Fig.  21,  and  is  known  as  the 
direct-coupling  method.  An  inductance  of  several  turns  of  wire  is, 
in  effect,  introduced  in  series  with  the  aerial  and  the  ground.  A 


Marconi-Braun  Inductive  Trans- 
mitting Antennae 


35 


36 


WIRELESS  TELEGRAPHY 


AERIAL 


CONDEN, 


certain  portion  of  the  inductive  turns  is  included  in  a  closed  oscilla- 
tory circuit  composed  of  a  condenser  and  spark  gap  shunted  around 
the  said  portion.  When  the  closed  energy-storing  oscillatory  cir- 
cuit and  the  open  radiating  circuit  of  the  aerial  are  adjusted  to  the 
same  periodicity  the  scheme  becomes  effective.  The  method  of 
direct  coupling  has  been  subjected  to  many  changes  at  the  hands 
of  inventors,  in  some  cases  becoming  almost  unrecognizable,  but  upon 

analysis  the  fundamental  idea 
shows  through.  It  is  to  be  noted 
that  with  both  the  direct  and 
inductively  coupled  systems,  syn- 
tony  between  the  open  and  closed 
circuits  is  essential. 

Both  of  the  foregoing  ar- 
rangements allow  the  possibility 
of  creating  in  the  aerial  far  great- 
er charging  electromotive  forces 
which,  in  properly  proportioned 
antennae,  increase  toward  the 
top  where  they  may  reach  a  value 
equivalent  to  hundreds  of  thou- 
sands of  volts  in  the  larger  in- 
stallations. Hence,  with  the 
adoption  of  this  form  of  trans- 
mitting arrangement,  it  became 
possible  to  radiate  a  series  of  well- 
sustained  oscillations  of  much 
greater  energy  than  ever  before, 

thus  still  farther  extending  the  distance  to  which  communication 
could  be  carried.  This  improvement  may  be  said  to  be  one  of  the 
greatest  advances  in  the  history  of  radiotelegraphy. 

Propagation  of  Waves  from  a  Grounded  Oscillator.  The  theory 
of  the  propagation  of  electric  waves  from  a  Hertz  oscillator  before 
given,  assumed  a  perfectly  symmetrical  isolated  oscillator  suspended 
in  space.  The  employment  of  the  grounded  oscillator  in  the  form 
of  an  earthed  aerial  now  exclusively  used  in  radiotelegraphy  neces- 
sitates a  modification  of  the  above  theory  in  order  to  meet  the  prob- 
lems arising  under  the  changed  conditions.  The  new  arrange- 


Fig.  21. 


"Direct-Coupled"  Inductive 
Antennae 


36 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY         37 

ment  was,  in  effect,  the  substitution  of  the  earth  for  one  of  the  capacity 
areas  of  a  Hertz  radiator,  and  the  extension  of  the  companion  area 
into  a  vertical  wire  possessing  capacity  with  regard  to  the  earth  from 
which  it  is  separated  by  an  air  gap.  The  type  of  wave  radiating 
from  such  a  system  differs  in  many  respects  from  the  form  of  dis- 
turbance emanating  from  a  simple  isolated  oscillator,  and  presents 
theoretical  difficulties  which  cannot  as  yet  be  said  to  be  satisfactorily 
explained.  The  electric  waves  from  a  grounded  oscillator  apparently 
follow  the  curvature  of  the  earth.  One  of  the  theories  purporting 


Fig.  22.    Diagrammatic  Representation  of  the  Sliding- Wave  Theory  of  Propagation 

to  account  for  this  phenomenon  assumes  that  such  waves  are  not 
ordinary  free  electric  waves  consisting  of  closed  loops  of  electric 
strain,  but  on  the  contrary  consist  of  half  loops  traveling  over  the 
surface  of  our  globe  with  their  ends  remaining  always  in  contact  with 
the  surface.  This  view  is  supported,  it  would  seem,  by  the  electronic 
theory  of  electricity.  It  is  roughly  represented  in  Fig.  22.  The 
detached  semi-loops  of  strain  are  shown  by  the  lighter  lines,  and 
the  simple  grounded  oscillator  by  the  heavier.  A  wave-length  would 
be  represented  on  the  horizontal  line  by  the  distance  included  be- 
tween any  two  positions  thereon  where  the  direction  and  intensity 
of  strain  (shown  respectively  by  the  arrows  and  the  proximity  of 
the  lines)  is  identical.  This  is  the  sliding-wave  theory,  said  to  have 


37 


38  WIRELESS  TELEGRAPHY 

been  first  promulgated  by  J.  E.  Taylor.  Other  theories  have  been 
advanced  to  account  for  the  wave-transmission  following  the  curva- 
ture of  the  earth,  one  such  assuming  that  the  waves  are  radiated  in 
a  straight  line  but  reflected  back  from  a  semi-conductive  envelope 
formed  by  the  upper  strata  of  the  earth's  atmosphere. 

Selective  Signaling.  The  problem  of  directing  a  message  to 
its  proper  destination  was  felt  by  early  investigators  to  be  of  vital 
importance,  if  radiotelegraphy  was  ever  to  be  a  commercial  success. 
Some  method  must  be  discovered  to  effect  selective  signaling — else 
how  would  it  be  possible  for  a  plurality  of  stations  to  be  transmitting 
at  once?  The  solution  of  the  difficulty  was  thought  to  be  found  in 
the  principle  of  resonance. 

The  history  of  the  subject  records  at  a  very  early  date  efforts 
to  achieve  the  desired  end  by  employing  definite  wave-lengths  corre- 
sponding to  the  electrical  time-periods  of  the  various  stations  it  was 
desired  to  place  into  communication.  Thus  among  a  plurality  of 
active  sending  stations  any  number  might  communicate  simultane- 
ously in  pairs  without  interference  by  arbitrarily  assigning  a  definite 
frequency,  or  wave-length,  to  each  pair.  Selection  by  this  method 
assumes  that  it  is  possible  to  "tune"  receiving  instruments  so  they 
will  respond  to  a  particular  "pitch"  and  to  no  other;  but  as  the  num- 
ber of  possible  non-interfering  wave-lengths  is  limited,  it  cannot  be 
said  that  resonance  offers  an  entirely  satisfactory  solution  of  the 
problem. 

By  the  employment  of  two  or  more  receiving  circuits  connected 
to  the  same  aerial,  each  tuned  to  a  different  frequency  correspond- 
ing to  as  many  different  sending  stations,  the  simultaneous  recep- 
tion of  two  or  more  messages  is  theoretically  possible.  As  early  as 
1900,  Marconi  achieved  some  very  remarkable  results  of  simultaneous 
non-interfering  communication  when  he  received  by  the  same  aerial 
two  messages,  one  in  English  and  the  other  in  French,  which  were 
simultaneously  transmitted  over  a  distance  of  30  miles. 

It  was  to  be  expected  that  the  last  few  years  would  bring  in  their 
train  great  improvements  in  this  respect  as  well  as  in  others,  so  that 
it  may  be  said  today  that  selective  signaling  is  feasible  to  a  certain 
extent  and  that  the  remaining  obstacles  will  be*  removed  by  further 
developments  of  the  art;  but  until  those  advances  are  made,  so  that 
much  more  can  be  accomplished  with  respect  to  selective  signaling 


THE  DEVELOPMENT  OF  RADIOTELEGRAPHY    39 

than  at  present,  the  field  of  operation  for  radiotelegraphy  will  be 
confined  mostly  to  communication  between  ships,  between  ships 
arid  shore,  and  across  large  bodies  of  water. 

Conclusion.  The  application  of  Hertzian  waves  to  the  pur- 
poses of  telegraphy  as  outlined  above,  covers  what  might  be  called 
the  foundation  and  early  development  of  the  art.  Every  step  taken 
at  this  early  period  was  vital  and  significant.  Since  then  enormous 
advances  have  been  made;  the  distances  over  which  it  is  possible  to 
telegraph  have  been  greatly  extended,  and  the  apparatus  rendered 
more  sensitive  and  certain  in  every  way;  but  these  results  have  been 
accomplished  more  by  a  refinement  of  detail — the  development  of 
more  sensitive  instruments,  and  the  closer  connection  between  theory 
and  practice — rather  than  by  the  application  of  fundamentally  new 
ideas.  The  twentieth  century  ushered  in  a  new  and  tentative  method 
of  telegraphic  communication  called  radiotelegraphy,  and  the  first 
ten  years  have  witnessed  its  establishment  as  one  of  the  permanent 
adjuncts  of  civilization, 


39 


CHAPTER  IV 
RADIOTELEGRAPHIC  APPARATUS 

It  is  obviously  impossible  within  the  scope  of  the  present  work 
to  give  a  detailed  description  of  all  the  apparatus  pertaining  to 
radiotelegraphy.  In  view  thereof  it  is  assumed  that  the  reader  is 
familiar  with  the  ordinary  instruments  and  physical  appliances 
commonly  used  in  electrical  work  and  not  in  any  way  peculiar  to 
wireless  telegraphy.  It  is  also  assumed  that  the  elementary  facts  of 
electrical  phenomena  are  known.  The  descriptions  of  the  apparatus 
in  this  chapter  will  be  given  without  reference  to  their  grouping  to- 
gether in  the  formation  of  a  complete  system,  but  will  be  given 
singly  with  such  theoretical  considerations  as  may  seem  necessary. 
The  chapter  following  will  be  given  over  to  the  assembling  of  apparatus 
into  complete  systems  under  their  proper  appellations,  together  with 
some  account  of  their  performance.  fc> 

Sources  of  Energy.  In  any  system  of  radiotelegraphy  the  prime 
desideratum  is  to  associate  with  the  aerial  a  maximum  amount  of 
energy  available  for  radiation.  It  was  early  recognized  that  the 
most  obvious  way  to  accomplish  this  was  to  increase  the  capacity 
of  the  aerial  or  to  employ  condensers  associated  in  various  ways  in 
order  to  store  temporarily  the  electrical  energy  to  be  radiated.  The 
main  function,  therefore,  of  the  source  of  energy  employed  in  the  trans- 
mitting station  is  to  properly  charge  a  given  capacity.  The  greater 
this  capacity,  the  greater  the  amount  of  initial  energy  required. 
Expediency  determines  largely  the  nature  of  the  source  of  energy, 
whether  derived  from  storage  batteries,  a  generator,  or  from  power 
mains.  The  energy  consumption  ranges  from  a  few  watts  up  to 
50  to  100  kilowatts,  so  it  is  evident  that  the  sources  of  current  are 
subject  to  a  wide  range  of  choice.  The  trans-Atlantic  stations  of 
Marconi  at  Cape  Breton  employ  generators  of  65  horse-power. 

Charging  Devices.  To  create  the  required  electrical  oscillations 
in  the  aerial,  it  is  necessary  to  have  appliances  which  shall  generate 
the  requisite  high-potential  electromotive  forces  for  charging  the 


40 


RADIOTELEGRAPHIC  APPARATUS  41 

aerial  and  its  associated  capacity.  Such  an  appliance  should  create 
not  only  a  high  potential  but  also  an  appreciable  current.  This 
charging  e.  m.  f.  is  generally  effected  by  the  use  of  the  induction  coil 
or  the  alternating-current  transformer. 

Induction  Coils.  It  is  not  deemed  necessary  to  give  an  extended 
discussion  of  the  induction  coil,  but  to  call  attention  to  the  important 
modifications  to  be  incorporated  therein  for  use  in  wireless  telegraphy. 
The  purpose  for  which  the  coil  is  employed  is  to  charge  a  condenser 
of  some  form  rapidly.  The  time  required  for  a  condenser  to  attain 
the  same  potential  as  the  charging  source  to  which  it  is  connected 
depends  largely  upon  the  resistance  of  the  charging  source.  In 
order  to  secure  a  small  time-constant  for  the  charging  circuit,  it  is 
highly  desirable  to  have  a  secondary  of  as  low  resistance  as  possible. 
The  lower  the  resistance  of  the  secondary,  the  greater  the  capacity 
that  can  be  rapidly  charged  by  a  coil  of  a  given  number  of  turns. 
It  must  be  borne  in  mind  that,  in  order  to  charge  a  condenser  to  a 
given  potential,  current  is  required.  The  usual  small  induction  coil 
is  wound  with  very  fine  wire  on  the  secondary — No.  36  or  finer.  It 
goes  without  saying  that  this  is  not  at  all  suited  for  use  in  wireless 
telegraphy.  Considerable  data  on  coils  suitable  for  the  use  herein 
considered  is  available.  The  core  should  be  composed  of  well- 
annealed,  Swedish  soft  iron  wire  of  small  diameter — about  No.  24 — 
wound  with  a  primary  of  comparatively  few  turns  of  coarse  copper 
wire — about  No.  12 — double  cotton-covered  and  well  insulated  from 
the  core.  It  is  not  practical  to  wind  the  secondary  with  coarser  wire 
than  No.  32  or  No.  33  B.  &  S.  gauge.  Special  attention  should  be 
paid  to  the  insulation  of  the  secondary  as  it  is  of  great  importance 
that  this  be  able  to  withstand  the  high  impulsive  electromotive  forces 
of  short  duration  which  occasionally  manifest  themselves.  Late  de- 
sign seems  to  be  in  the  direction  of  longer  cores — about  twice  the 
length  of  the  secondary  winding. 

Tesla  called  attention  to  a  fact  of  importance  in  connection 
with  induction-coil  design,  as  far  back  as  1893,  viz,  that  a  condition 
of  resonance  between  the  primary  and  the  secondary  circuits  greatly 
adds  to  the  efficiency  of  the  device.  This  has  the  practical  result 
of  greatly  decreasing  the  resistance  of  the  secondary  and  also  the 
number  of  turns,  with  a  result  that  much  more  current  is  deliverable 
from  such  a  coil.  In  the  primary  circuit  there  is  usually  large  capacity 


41 


42 


WIRELESS  TELEGRAPHY 


SPARK  GAP 


COKS 


and  small  inductance,  while  in  the  secondary  there  is  small  capacity 
and  large  inductance. 

Even  with  the  above  added  efficiency,  induction  coils  are  not 
as  suitable  in  many  respects  for  commercial  radiotelegraphy  as 
alternating-current  transformers.  The  utility  of  the  induction  coil 
is  limited  by  reason  of  the  fact  that  the  details  of  design  are  so  largely 
a  matter  of  compromise  that  it  is  impracticable  to  obtain  the  desired 
charging  current  at  the  required  voltage.  The  efficiency  of  induction 
coils  is  at  best  but  slightly  above  50  per  cent,  and  there  are  reasons 
for  believing  it  much  lower. 

The  three  important  adjuncts  of  the  induction  coil  are  the  pri- 
mary condenser,  the  interrupter,  and  the  signaling  key. 

Primary  Condenser.  The  principal  function  of  the  primary 
condenser  is  to  absorb  the  energy  that  manifests  itself  at  break  in 

the  form  of  an  arc,  due  to  the 
self-induction  of  the  primary  cir- 
cuit. As  the  secondary  e.  m.  f. 
is  due  largely  to  the  suddenness 
of  the  rupture  in  the  primary,  it 
is  qf  the  utmost  importance  that 
this  arc  be  prevented  from  form- 
ing. The  primary  condenser  is, 
therefore,  placed  across  the  break 
jn  Sucj1  a  manner  as  t0  ke  short- 

circuited     when    the    circuit 


s 

closed,    but    at    the    instant    of 
break   it  is  placed  in  the  circuit 

and  absorbs  the  energy  which  would  otherwise  be  dissipated  in 
the  formation  of  an  arc,  and  which  would  very  greatly  increase  the 
time  of  rupture.  Fig.  23  indicates  the  arrangement  of  the  circuit. 
The  best  value  for  the  primary  condenser  is  that  capacity  which 
will  annul  to  the  greatest  degree  the  sparking  at  the  points  of  the 
interrupter.  Experiments  have  shown  that  if  the  primary  be  broken 
with  sufficient  rapidity,  as  for  instance  with  a  rifle  ball,  no  condenser 
is  needed.  A  condenser  is  not  needed  with  a  Wehnelt  interrupter. 

Interrupters.  Interrupters  perform  the  sole  function  of  causing 
a  rapid  succession  of  sudden  breaks  in-  the  primary  circuit.  The 
commonest  as  well  as  the  oldest  form  of  break  is  known  as  the  hammer 


Fig.  23.    Diagram  of  Induction  Coil 
Showing  Condenser  Circuit 


RADIOTELEGRAPHIC  APPARATUS 


43 


break,  probably  invented  by  Neef.  Its  action  is  perhaps  best  shown 
by  referring  to  the  common  electric  door-bell.  An  electromagnet, 
in  attracting  an  armature,  causes 
an  interruption  of  the  current 
energizing  the  electromagnet, 
whereupon  the  armature  falls 
back  by  reason  of  its  spring 
tension  and  again  completes  the 
circuit;  this  energizes  the  magnet 
once  more,  which  again  attracts 
the  armature,  and  the  whole 
operation  is  repeated.  The  arm- 
ature is  thus  kept  in  continual 
vibration  with  consequent  inter- 
ruptions of  the  current.  Fig.  24 
shows  this  device — which  is  sub- 
ject to  almost  endless  variation 


—  in  a  form  having  as  one  of 
its  decided  advantages  the  ease 
with  which  it  is  adjusted  by 

simple  regulation  for  different  frequencies.  Fig.  25  shows  an- 
other form  with  the  contacts  made  in  small  cups  of  mercury,  known 
as  the  Foucault  break.  It  is  obvious  that  the  break  can  be 
produced  independently  of  the 
current  in  the  primary  circuit 
by  means  of  a  small  electric 
motor  acting  on  a  lever  which  is 
made  to  dip  into  a  cup  of  mer- 
cury, thus  completing  the  circuit 
any  desired  number  of  times  per 
revolution.  Such  a  break  is 
called  the  motor  break.  The 
rotary,  or  turbine,  break  has 
been  used  very  successfully  on 
large  coils  requiring  considerable 
amperage  for  their  operation.  The  simple  hammer  break  does 
not  operate  well  with  voltages  over  16  or  20;  therefore,  when  it  be- 
comes necessary  to  utilize  commercial  pressures  such  as  110  and 


Fig.  24.     Neef  Hammer  Break 


Fig.  25.    Foucault  Mercury  Break 


43 


44 


WIRELESS  TELEGRAPHY 


220  volts,  some  form  of  mercury  turbine  interrupter  is  found  to  be 
preferable.     One  form  of  this  interrupter  is  shown  in  Fig.  26. 

Dr.  Wehnelt  of  Charlottenburg  invented,  in  1899,  a  form  of 
interrupter  for  use  with  induction  coils,  operating  on  an  entirely 
different  principle  from  those  described  above.  Taking  two  elec- 
trodes of  very  different  size,  such  as  a  large  lead  plate  and  a  small 
piece  of  platinum  wire  projecting  from  the  end  of  a  closely  fitting 
glass  tube,  and  placing  them  in  an  electrolyte  of  dilute  sulphuric 
acid,  he  discovered  that  an  electrolytic  action  takes  place  when  the 


Fig.  26.     Mercury  Turbine  Interrupter 

large  lead  plate  is  made  the  negative  pole,  this  action  interrupting 
the  current  periodically  when  the  device  is  connected  to  a  source  of 
40  to  80  volts.  Fig.  27  gives  an  idea  of  the  device,  showing  one  of 
the  many  modifications  it  has  undergone  in  its  commercial  design. 
The  positive  platinum  electrode  can  be  seen  protruding  slightly  from 
the  end  of  the  porcelain  insulating  tube  immersed  in  the  liquid,  which 
must  be  a  solution  of  about  one  part  sulphuric  acid  to  ten  parts  of 


44 


RADIOTELEGRAPHIC  APPARATUS 


45 


water.  The  cut  shows  a  water-cooling  jacket,  which  is  an  advantage 
as  the  apparatus  becomes  very  warm  under  continued  use.  Ex- 
periments have  shown  this  device  to  be  capable  of  producing  an  in- 
termittency  of  over  1,800  per  second.  As  mentioned  above,  no  con- 
denser is  necessary  when  opera- 
ting an  induction  coil  with  this 
form  of  interrupter.  The  char- 
acter of  the  secondary  discharge 
is  somewhat  changed  by  the  use 
of  the  Wehnelt  cell,  rendering  it 
more  like  the  alternating  arc  than 
the  usual  disruptive  spark.  It 
cannot  be  said  that  an  entirely 
satisfactory  theory  has  ever  been 
given  for  the  action  of  this  cell. 
The  Wehnelt  interrupter  has  not 
been  used  very  commonly  in 
connection  with  radiotelegraphic 
work,  its  greatest  field  of  useful- 
ness being  in  Rontgen  ray  work. 

Keys.  In  order  to  transmit  messages  by  means  of  an  arbitrary 
code  consisting  of  long  and  short  trains  of  waves  representing  the 
Morse  alphabet,  an  adequate  means  of  controlling  the  torrent  of 
sparks  between  the  electrodes  of  the  spark  gap  must  be  employed. 
The  key  problem  in  this  form  of  telegraphy  is  somewhat  more  com- 
plicated than  in  the  ordinary  wire  systems,  primarily  by  reason  of 
the  fact  that  a  much  greater  current  must  be  controlled.  The  com- 
mon Morse  key  need  not  open  more  than  a  fraction  of  an  inch,  ^T 
being  ample;  but  it  becomes  necessary  in  wireless  work  to  rapidly 
break  currents  of  several  amperes  in  circuits  of  considerable  inductance, 
under  which  conditions  the  Morse  key  would  not  answer  at  all. 
The  speed  of  signaling  depends  largely  on  the  rapidity  of  the  key, 
a  wide  movement  greatly  cutting  down  the  efficiency  of  the  system 
as  a  means  of  communication;  therefore,  short-range  keys  must  be 
provided,  with  some  means  of  annulling  the  heavy  spark  on  break. 
Many  suggestions  have  been  made  and  a  number  of  patents  taken 
out  purporting  to  accomplish  this  end.  The  magnetic  blow-out  has 
proved  the  most  generally  useful;  though  some  systems  employ  a 


Fig.  27.     Wehnelt  Interrupter 


45 


46 


WIRELESS  TELEGRAPHY 


short-circuiting  resistance  around  the  break,  and  others  a  condenser 
to  absorb  the  arc.  One  form  of  Marconi  key  simultaneously  breaks 
the  primary  current  and  disconnects  the  aerial  from  the  transmitting 

apparatus.  Many  keys  are  de- 
signed to  cause  the  break  to 
take  place  under  oil  or  other 
highly  insulative  substances. 
Lodge  and  Muirhead  employ  an 
electromagnetically  operable  key 
which  is  actuated  by  current  in 
a  local  circuit  interrupted  by  an 
ordinary  Morse  key.  A  common 
form  of  such  a  key,  which  is  of 

Fig.  28.    Long  Range  Morse  Key  yery   heayy   construction   and    of 

extra  wide  movement,  is  shown  in  Fig.  28. 

Alternating=Current   Transformers.    In   nearly   all   high-power 
stations  it  has  been  found  advantageous,  if  not  absolutely  necessary, 
to  discard  the  induction  coil  as  a  means  of  charging  the  high  capacities 
used,    substituting    the    alternating-current    transformer,     This    in- 
volves the  employment  of  an  alternating-current  as  the  initial  source 
of  power.     Transformers  designed  for  this  purpose  are  wound  for 
a  high  ratio  of  transformation,  generally  for  a  secondary  voltage  of 
at  least  20,000  volts,  and  often  30,000  to  50,000.     A  difficulty  expe- 
rienced with  the  use  of  the  transformer 
is  the  liability  of  forming  an  alternating 
arc  between  the  balls  of  the  gap  in  place 
of   the  proper   oscillatory    spark.     The 
practical    short-circuiting   of    the   trans- 
former by  this  action  causes  a  great  rush 
of  current   through  the  primary,  which, 
if  it  has   not  been  guarded  against,  is 
liable  to  cause  great  havoc  with  the  gen- 
erator, blowing  out  the  fuses  and  possi- 
bly working  other  damage  more  serious. 
When    the   capacity    of    the    condenser 

is  of  the  exact  value  to  take  up  in  the  form  of  a  charge  nearly  the 
entire  energy  of  each  half-wave  of  the  periodic  current,  no  alternating 
arc  will  arise  and  the  discharge  across  the  gap  will  be  due  entirely  to 


Fig.  29.     Tesla  Magnetic 
Blow-out 


46 


RADIOTELEGRAPHIC  APPARATUS  47 

the  condenser,  in  which  case  no  external  means  for  extinguishing  the 
arc  are  necessary;  but  this  relation  is  very  hard  to  effect  permanently, 
so  that  numerous  plans  have  been  devised  to  prevent  the  formation 
of  this  arc.  The  one  due  to  Nikola  Tesla,  which  has  undoubtedly 
proved  to  be  the  best,  utilizes  a  strong  electromagnet  so  that  its  lines 
of  force  pass  transversely  between  the  spark  gap.  This  arrange- 
ment is  called  a  magnetic  blow-out.  Fig.  29  shows  the  scheme. 
Elihu  Thomson  achieves  the  same  end  by  directing  a  strong  blast 
of  air  on  the  gap  from  a  nozzle.  This  permits  the  oscillatory  spark 
to  form  at  the  proper  time,  but  completely  extinguishes  the  alter- 
nating arc,  or  rather  prevents  its  formation.  The  noise  incident 
to  the  operation  of  a  large  transformer  producing  a  heavy  oscillatory 
spark  is  deafening  and  some  precaution  must  be  taken  to  protect 
the  ears  of  an  attendant  if  the  gap  is  not  enclosed.  The  light  from 
such  a  spark  is  also  very  hard  on  the  eyes. 

Oscillation  Transformers.  Transformers  designed  for  high- 
frequency,  high-potential,  oscillatory  currents  are  in  many  respects 
different  from  the  transformers  suitable  for  use  on  low-pressure, 
low-frequency,  electric-light  mains.  The  most  striking  difference 
is  the  absence  of  an  iron  core  and  the  small  number  of  turns  of  wire 
employed.  The  transformer  used  by  Marconi  with  the  Marconi- 
Braun  type  of  closed  oscillator  was  constructed  as  follows:  The 
primary  consisted  of  but  one  turn  on  a  stranded  conductor  of  low 
resistance  with  a  secondary  of  thinner  wire  laid  over  the  primary  in 
about  ten  turns.  The  coils  wTere  immersed  in  highly  insulating  oil. 
In  commercial  practice  oscillation  transformers  are  of  various  design. 
It  is  of  the  utmost  importance  that  transformers  of  this  character  be 
specially  well  insulated,  particularly  when  the  primary  and  the 
secondary  are  in  close  inductive  relation.  The  use  of  oil  in  this  con- 
nection is  the  common  practice.  Late  forms  of  oscillation  trans- 
formers are  made  in  such  a  manner  that  the  distance  between  the 
primary  and  the  secondary  may  be  varied,  thus  alternating  their 
inductive  relation,  a  so-called  "loose  couple"  being  produced  by 
separating  the  two  components. 

Condensers.  The  condensers  employed  in  radiotelegraphy, 
as  in  other  departments  of  electro-technics,  are  chosen  with  regard 
to  the  voltages  to  which  they  are  to  be  subjected.  The  capacity  used 
in  connection  with  receiving  circuits  requiring  no  high  insulating 


47 


48  WIRELESS  TELEGRAPHY 

properties  generally  takes  the  form  of  paper  or  mica  condenser  sup- 
plemented by  a  variable-capacity  condenser  consisting  of  a  number 
of  fixed  metallic  plates  interspaced  in  air  between  an  equal  number 
of  moveable  plates,  whereby  the  effective  capacity  areas  of  the  plates 
may  be  varied  within  wide  limits. 

In  the  transmitting  circuit  where  the  condenser  is  employed  to 
temporarily  store  the  energy  preparatory  to  the  sending  of  a  signal, 
a  form  of  condenser  must  be  used  which  will  withstand  the  electro- 
static strain  of  a  very  high  potential.  This  necessitates  the  use  of 
glass,  mica,  or  oil,  as  experience  has  proved  these  materials  to  be 
almost  the  only  dielectrics  practicable  for  the  purpose,  glass  being, 
all  things  considered,  the  best  of  all.  The  higher  the  voltage,  the 
greater  the  thickness  of  glass  needed;  and  as  the  storing  power  of  a 


»^ 

Fig.  30.     Adjustable  Condenser 


condenser  varies  directly  with  the  square  of  the  potential  to  which 
it  is  charged,  it  is  evident  that  there  exists  a  definite  relation  between 
the  dielectric  strength  of  the  medium  (glass)  and  the  volume  per 
unit  of  energy  which  it  is  desired  to  store.  This  is  equivalent  to 
saying  that  a  great  amount  of  energy  could  be  stored  in  a  very  small 
condenser  if  the  dielectric  could  stand  an  exceedingly  high  potential. 
Hence,  the  object  to  be  attained  in  the  designing  of  condensers  for 
radiotelegraphy  is  a  maximum  energy-storing  ability  with  a  minimum 
of  cost,  size,  and  weight  of  glass.  In  practice  it  is  better  to  use  a  good 
grade  of  glass  free  from  lead  and  other  impurities.  Oil  condensers 
are  sometimes  used,  constructed  of  sheets  of  brass  or  zinc,  and  im- 
mersed in  "transformer  oil."  Adjustable  condensers,  made  as  shown 
in  Fig.  30,  are  often  used  for  purposes  of  tuning;  their  capacity  may 
be  varied  by  withdrawing  the  plates,  thereby  reducing  the  effective 
area.  Braun  employed  small  condensers  made  of  test-tubes  covered 
with  tin-foil  inside  and  out  for  short-distance  low-power  stations. 


48 


RADIOTELEGRAPHIC  APPARATUS  49 

Quart  or  gallon  Leyden  jars  are  often  employed,  lending  themselves 
very  well  to  the  requirements. 

Tuning  Coils.  In  order  to  facilitate  the  tuning,  or  syntonizing,  of 
the  oscillatory  circuits  included  in  a  system  of  radiotelegraphy,  some 
apparatus  for  varying  the  electrical  dimensions  of  such  a  circuit  is 
usually  employed.  These  tuning  devices  consist  simply  of  a  variable  in- 
ductance, or  of  an  adjustable  condenser  to  vary  the  capacity,  or  of  both 
embodied  in  a  single  piece  of  apparatus.  As  the  inductance  factor 
lends  itself  more  readily  to  a  simple  method  of  variation,  numerous 
forms  of  adjustable  inductance  coils  have  been  devised,  the  design 
of  which  depends  upon  the  circuit  they  are  to  be  employed  with. 

Tuning  coils  for  use  with  the  transmitting  side  of  a  station  are 
characterized  by  a  comparatively  few  turns  of  very  heavy  wire  or 
metal  ribbon  wound  spirally  on  an  insulated  drum  or  ebonite  cylinder. 
Connection  is  made  at  any  point  on  the  spiral  conductor  either  by 
means  of  flexible  connecting  cords  provided  with  metallic  clips,  or 
by  the  use  of  a  sliding  connection  so  arranged  as  to  permit  of  any 
desired  length  of  the  inductive  conductor  being  included  in  the  circuit. 
Many  systems  utilize  the  space  within  the  turns  of  inductive  resist- 
ance for  the  placing  of  the  condensers,  thus  greatly  economizing  the 
room  otherwise  required  for  these  two  portions  of  the  apparatus. 

As  the  receiving  circuits  usually  possess  much  less  capacity 
than  the  transmitting  circuits,  the  tuning  coils  designed  for  connec- 
tion therewith  have  a  much  larger  number  of  turns.  Such  coils 
are  generally  constructed  with  several  hundred  turns  of  rather  fine 
wire  wound  on  a  large  bobbin  having  two  sliding  contacts  so  arranged 
as  to  include  between  them  any  desired  number  of  turns.  These 
coils  are  made  in  a  great  variety  of  ways. 

Spark  Gaps.  An  important  element  of  the  transmitting  station 
is  the  gap,  across  which  the  stream  of  sparks  takes  place.  In  a  previous 
chapter  attention  has  been  called  to  the  resonator  of  Hertz  and  to 
the  metallic  balls  between  which  he  produced  his  oscillatory  spark. 
In  his  book  on  "Electric  Waves"  published  in  English  in  1894,  he 
advises  that  these  balls  be  highly  polished.  For  the  small  amount 
of  energy  used  by  Hertz  this  was  no  doubt  advantageous,  particularly 
in  the  production  of  short  waves;  but  with  the  further  development 
of  the  art  it  became  evident  that  it  was  impossible  to  maintair 
such  surfaces  when  employing  sparks  of  great  volume.  The  essen- 


50 


WIRELESS  TELEGRAPHY 


tial  condition  to  be  fulfilled  is  that  the  discharging  surfaces 
shall  maintain  a  permanent  condition  and  not  be  burned  away  and 
pitted  by  the  rapidly  recurring  heat  of  the  spark.  With  the  utiliza- 
tion of  radiators  of  high  power,  and  with  the  employment  of  trans- 
formers capable  of  charging  large  capacities,  the  need  of  a  means 
for  maintaining  a  constant  condition  of  the  spark  gap  became  im- 
perative. Special  appliances  were  devised  to  prevent  the  pitting  of 
the  balls  and  their  consequent  destruction. 

Marconi  early  adopted  the  Righi  oscillator  plan  of  placing  the 
balls  in  a  chamber  of  oil,  or  other  highly  insulative  medium,  thereby 
excluding  the  oxygen  of  the  air  from  the  balls  and  preventing  oxidiza- 
tion. He  soon  found,  however,  that  the  insulating  fluid  was  rapidly 
decomposed  under  the  influence  of  the  more  powerful  discharges 
and  abandoned  the  idea  in  favor  of  a  "dry"  ball  system. 

Numerous  inventors  have  contrived  many  so-called  multiple- 
ball  exciters,  among  whom  is  J.  S.  Stone,  whose  oscillator  is  shown 
in  Fig.  31.  R.  A.  Fessenden  has  conducted  numerous  experiments 

which  seem  to  indicate  that  there  is  great 
advantage  to  be  gained  by  causing  the 
spark  to  take  place  in  a  compressed-air 
chamber.  This  is  explained  by  the  fact 
that  the  effective  potential  between  the 
balls  is  thereby  raised  without  rendering 
the  spark  non-oscillatory.  Better  radia- 
tion is  possible  also,  according  to  Fes- 
senden, and  it  is  undoubtedly  a  great 
improvement  in  reducing  the  ear-splitting 
noise  of  the  customary  discharge.  Various  compressed  gases  have 
also  been  used  with  varying  success. 

Among  the  various  forms  of  exciter  which  have  more  or  less 
successfully  fulfilled  the  requirements,  mention  must  be  given  to  one 
other  fundamental  form  employed  by  Marconi.  It  took  advantage 
of  the  important  fact  that  though  it  is  exceedingly  difficult  to  create 
a  true  alternating  arc  between  two  relatively  moving  surfaces,  never- 
theless an  electric  oscillation  from  a  condenser  can  readily  take  place 
even  though  the  movement  be  exceedingly  rapid.  Marconi,  there- 
fore, devised  what  is  known  as  the  high-speed  disk  discharger,  shown 
in  Fig.  32.  It  would  seem  that  this  design  of  gap  possesses  many 


Fig.  31.    Multiple-Ball  Exciter 


50 


RADIOTELEGRAPHIC  APPARATUS 


51 


advantages  as  attested  by  the  extensive  employment  of  it  at  the  trans- 
Atlantic  stations.  The  illustrations  make  clear  the  connections. 
The  apparatus  consists  of  two  metallic  disks  A  and  B,  revolving 
at  high  speed,  and  a  second  larger  disk  at  right  angles  to  the  axis  of 
the  other  two  and  between  them,  also  revolving  at  high  speed.  There 
are  thus  two  gaps  where  sparks  may  take  place.  The  closing  of  the 
key  charges  the  condensers  C  and  D,  in  series  between  which  is  con- 
nected the  condenser  E,  which  discharges  the  energy  across  either 


AER/AL 


EARTH 

Fig.  32.     Diagram  of  Marconi  High-Speed  Disk  Discharger 

gap  between  the  rapidly  revolving  terminals.  Another  modification 
of  this  device,  shown  in  Fig.  33,  is  characterized  by  the  fact  that  it  is 
designed  for  use  with  a  direct  current.  The  mechanical  construc- 
tion is  similar  to  that  of  the  form  previously  described,  with  the  ex- 
ception that  the  large  disk  has  a  row  of  metallic  studs  placed  equi- 
distantly  around  its  circumference  in  such  a  manner  as  to  greatly 
shorten  the  length  of  the  air  gap  between  the  two  revolving  terminals 


51 


52 


WIRELESS  TELEGRAPHY 


when  the  said  studs  occupy  a  position  in  a  line  with  the  plane  of  their 
rotation.  The  office  of  these  studs  is  to  shorten  the  air  gap  at  pre- 
determined and  equal  intervals,  thus  discharging  the  condensers, 
which  are  immediately  charged  by  the  direct  current.  In  both  forms 
of  the  device  the  arc  is  prevented  by  the  rapid  rotation  of  the  revolv- 
ing parts.  It  is  claimed  that  the  Marconi  dischargers  permit  of  great 
rapidity  of  signaling.  The  last  described  produces,  when  run  at  very 
high  speed,  an  almost  continuous  train  of  oscillations. 


AER/AL 


D/ffECT 
CURRENT 


XEVOLV/NG  DISK 


$TL/DS        EARTH 

Fig.  33.     Disk  Discharger  for  Use  with  Direct  Current 

High-Frequency  Alternators.  It  was  known  at  an  early  date 
in  the  history  of  radiotelegraphy  that  a  much  greater  efficiency  could 
be  achieved  if  a  means  were  devised  for  creating  a  continuous  train 
of  undamped  oscillations.  The  Morse  dot,  which  is  the  minimum 
signal,  was  seen  to  be  composed  of  a  considerable  number  of  separate 
trains  of  waves,  each  rapidly  damped.  Could  these  "gaps"  in 
the  wave  train  be  filled  up,  the  received  signal  would  not  only  be 


52 


RADIOTELEGRAPHIC  APPARATUS  53 

stronger,  but  selective  signaling  would  also  be  greatly  facilitated 
and  precise  tuning  be  more  easily  accomplished.  A  moment's 
thought  will  suffice  to  convince  that  a  continuous  train  of  undamped 
oscillations  would  be  the  exact  equivalent  of  a  continuous  alternating 
current  of  extremely  high  frequency;  and  this  opens  up  the  possibility 
of  employing  generators  which  might  be  connected  directly  with  the 
aerial,  thus  doing  away  with  the  intermediate  condenser  and  spark 
gap. 

Many  attempts  have  been  made  to  construct  generators  df  suf- 
ficiently high  frequency,  the  majority  of  them  having  been  of  the  in- 
ductor type.  An  exceedingly  small  electrical  output  seems  to  be  the 
characteristic  of  all  attempts  thus  far  to  produce  such  a  machine. 
Great  speed  of  rotation  of  the  disk  armature  is  required  in  this  type 
of  generator,  and  as  there  are  limits  beyond  which  it  is  unsafe  to  push 
the  rotation,  fundamental  difficulties  arise  which  have  not  as  yet  been 
surmounted  with  any  degree  of  commercial  success.  Fessenden 
claims  to  have  produced  an  alternator  giving  a  frequency  of  80,000 
cycles.  The  wattage  is  said  to  be  about  250.  The  ingenious  Ger- 
man inventor,  Ernst  Ruhmer,  has  also  constructed  an  alternator 
of  the  inductor  type  having  a  frequency  of  300,000  and  an  output 
of  but  .001  watt;  and  W.  Duddell  has  succeeded  in  producing  a 
frequency  of  120,000  with  somewhat  greater  power.  Until  it  is 
possible  to  greatly  increase  the  output  of  such  machines,  their  use 
will  be  limited  to  laboratory  experiments,  or  at  most  to  short- 
distance  work  in  connectior  with  rs  iiotelegraphy.  Their  develop- 
ment at  the  present  time  seems  to  be  in  connection  with  radio- 
telephony. 

The  Singing  Arc.  Much  more  successful  have  been  the  attempts 
to  produce  a  continuous  train  of  undamped  oscillations  from  a  direct 
current,  Elihu  Thomson  applied,  in  1892,  for  a  United  States  patent 
en  a  method  intended  to  effect  such  a  transformation,  Fig.  34.  A 
source  of  direct  current  is  connected  to  a  circuit  having  a  very  high 
inductance,  and  a  spark  gap  across  which  is  shunted  a  condenser, 
and  smaller  inductance  in  series.  The  inventor  claims  in  his  patent 
specifications  that  the  gap,  inductance,  and  capacity  can  be  so  ad- 
justed that  the  condenser  is  periodically  discharged  across  the  gap 
at  frequencies  as  high  as  40,000  per  second. 

The  form  that  this  apparatus  has  since  taken  is  known  by  the 


53 


54 


WIRELESS  TELEGRAPHY 


name  of  Duddell  singing  arc,  on  account  of  the  further  developments 
introduced  by  him  in  1900.  Duddell  substituted  a  carbon  arc  for 
the  gap,  and  found  that  such  an  arrangement  produced  a  clear 


OSCILLATORY 
C/RCU/T 


Fig.  34.     Thomson  Direct-Current  Method  of  Generating 
Oscillations 

musical  note  plainly  audible  some  distance  away,  the  pitch  of  the 
note  depending  on  the  value  of  the  capacity  and  the  inductance  in  the 
oscillatory  circuit — the  latter  is  represented  by  the  heavier  lines  in 
Fig.  35.  The  best  effects  were  obtained  by  the  use  of  solid  rods  of 


OSCILLATORY 
CIRCUIT 


Fig.  35.     Duddell  Singing  Arc 

carbon.  The  resistance  of  the  inductance  in  the  oscillatory  circuit 
must  be  low — about  1  ohm.  Duddell  found  it  difficult  to  produce 
oscillations  of  any  considerable  power  above  a  frequency  of  about 
10,000;  although  other  experimenters  have  succeeded  in  reaching 
a  frequency  of  400,000  with  small  capacity  and  little  energy. 

It  remained  for  Valdemar  Poulsen  of  Copenhagen  to  make  the 
greatest  improvement  in  the  direct-current  arc  method  of  producing 


54 


RADIOTELEGRAPHIC  APPARATUS 


55 


oscillations.  Fig.  36  shows  Poulsen's  arrangement.  In  the  first 
place,  he  enclosed  the  arc  in  an  air-tight  chamber  filled  with  coal 
gas,  and  used  a  water-cooled  positive  electrode  with  a  carbon  negative. 
He  also  introduced  into  the  chamber  the  polar  projections  of  two 
powerful  electromagnets  in  such  geometrical  relation  as  to  cause  the 
lines  of  force  to  pass  directly  between  the  electrodes  as  shown  in  the 
diagram.  The  connecting  lines  make  clear  the  circuit.  The  funda- 
mental similarity  to  Thom- 
son's circuit  is  apparent.  It 
is  possible  to  produce  very 
powerful  undamped  oscilla- 
tions with  this  apparatus,  the 
frequency  of  which  may,  by 
the  proper  adjustment  of  the 
capacity  and  the  inductance, 
be  made  as  high  as  1,000,000 
or  more.  There  is  a  partic- 
ular length  of  arc,  called  the 
"active"  arc,  which  gives  the 
best  results.  Poulsen's  de- 
vice is  operable  with  many 
other  gases  besides  the  one 
mentioned.  The  magnets  S 
and  N  must  be  very  power- 
ful. 500  volts  seems  to  be  a  practical  voltage  for  use  with  this  device. 
Aerials.  The  aerials  at  present  used  are  of  many  kinds,  ranging 
from  the  short  length  of  weatherproof  wire  extending  from  an  upper 
window  to  a  nail  in  the  chimney,  proclaiming  the  abode  of  a  juvenile 
experimenter,  to  those  enormous  structures  taxing  the  resources 
of  modern  engineering  in  their  construction,  which  achieve  trans- 
Atlantic  communication.  It  was  early  recognized  that  the  radius 
of  communication  was  greatly  extended  by  increasing  the  capacity  of 
the  aerial;  which  fact  has  led  to  the  employment  of  multiple-wire 
antennae.  Figs.  37,  38,  39,  and  40,  show  some  of  the  commoner 
forms,  conditions  usually  determining  the  choice.  It  was  found  by 
experiment  that  the  capacity  of  two  wires  suspended  in  the  air  was 
not  twice  the  capacity  of  one,  nor  four  wires  twice  the  capacity  of 
two,  if  such  wires  were  placed  near  together.  The  reason,  therefore, 


Fig.  36.     Poulsen  Direct-Current  Method  of 
Generating  Oscillations 


55 


56 


WIRELESS  TELEGRAPHY 


is  apparent  why  in  many  of  the  aerials  the  individual  wires  are 
separated  to  comparatively  great  distances. 

It  is  of  extreme  importance  that  the  upper  end  of  suspended 
radiator  wires  should  be  exceptionally  well  insulated,  and  the  reason 
is  obvious.  Specially  designed  porcelain  or  glass  insulators  are 
used,  having  two  holes  through  which  the  ends  of  the  wires  are  bound. 

Aluminum  wire  serves  excellently  for  the  purpose  of  antennae 
when  the  strain  upon  it  is  not  too  great.  Its  low  tensile  strength 


^^ 

i 


Fig.  37. 


Fig.  38.  Fig.  39. 

Standard  Forms  of  Aerial 


Fig.  40. 


precludes  its  use  in  some  cases.  A  simple  manner  of  suspending 
a  single-wire  experimental  aerial  is  shown  in  Fig.  41.  The  mast,  or 
short  flag-pole,  may  be  lashed  to  the  tallest  object  available  and 
the  wire  carried  out  of  perpendicular  a  sufficient  distance  to  pre- 
vent it  from  hitting  the  pole.  In  army  field-equipment,  kites  or 
captive  balloons  are  often  used  to  elevate  the  aerial  wire,  which 
is  carried  wound  upon  a  reel.  Many  aerials  are  arranged  with  a 
tail  block  on  a  cross-tree  in  order  that  they  may  be  let  down  from  a 
high  mast  for  inspection  purposes.  Such  aerials  are  of  the  cage 
variety  shown  in  Fig.  38.  An  idea  of  the  construction  of  antennae 
when  designed  for  use  in  connection  with  high-power  stations  may 
be  gained  from  Fig.  42. 


56 


RADIOTELEGRAPHIC  APPARATUS 


57 


Directive  Antennae.  Many  efforts  have  been  made  to  direct 
the  transmission  of  radiotelegraphic  signals  to  any  desired  point  or 
locality,  but  with  indifferent  success. 
Early  attempts  embodied  the  use  of  large 
reflectors  behind  the  oscillator;  but  the 
most  encouraging  results  have  been  ac- 
complished by  the  use  of  what  are  known 
as  horizontal  antennae,  the  subject  of  a 
patent  granted  to  Marconi  and  dated 
1904.  DeForest  has  also  met  with  some 
success  along  this  line.  The  results  ob- 
tained by  these  investigators  are  not 
formulated  well  enough  as  yet  to  war- 
rant a  description  of  them  here. 

Detectors.  The  subject  of  the  re- 
ception of  wave-trains  and  the  transfor- 
mation of  their  energy  into  visual  or 
audible  signs  through  the  agency  of  suit- 
able translating  devices  will  now  be  taken 
up  and  described.  It  is  helpful  toward  a 
comprehension  of  this  part  of  the  subject 
to  get  clearly  in  mind  the  primary  effect 
of  a  train  of  waves  upon  a  receiving  aerial,  namely,  the  creation  of  an 


Fig.  41.     Single  Wire  Experi- 
mental Aerial 


Fig.  42.     Antennae  Construction  for  High-Power  Station 

alternating  electromotive  force.     And  the  prime  function  of  a  receiv- 
ing device  is  broadly  to  detect  the  presence  of  a  high-frequency 


57 


58 


WIRELESS  TELEGRAPHY 


alternating  current  of  minute  value.  Volumes  could  be  written  on 
the  history  of  the  various  forms  of  receiving  devices  which  have 
occupied  the  attention  of  the  various  investigators  in  this  interesting 
field  of  experiment.  In  the  present  instance  attention  will  be  called 
to  those  forms  only  which  have  proved  themselves  of  practical  value. 

Wave-detecting  devices  may  be  classified  for  convenience 
according  to  the  physical  principle  on  which  they  act,  such  as  thermo- 
electric, magnetic,  electrolytic,  chemical,  photo-electric,  physiological, 
etc.  This  course  will  be  followed  as  far  as  practicable. 

Coherers.  Coherers  work  on  the  principle  of  imperfect  contact 
and  are  called  self-restoring  and  non-restoring  according  as  their  sensi- 


FLAN 


Fig.  43.    Lodge-Muirhead  Detector 


tiveness  is  automatically  reassumed  after  the  passage  of  a  train  of 
waves,  or  must  be  superinduced  by  some  external  agency.  Com- 
mercially the  coherer  has  become  almost  obsolete. 

Branly  Coherer: — It  is  unnecessary  at  this  point  to  give  more 
than  passing  mention  to  the  Branly  coherer,  as  it  has  been  fully 
described  in  a  previous  chapter.  As  improved  by  Lodge  and  Mar- 
coni it  performed  a  very  important  function  in  the  early  days  of  radio- 
telegraphy,  but  has  now  fallen  into  disuse. 

Lodge-Muirhead  Coherer: — An  interesting  form  of  contact 
detector  is  shown  in  Fig.  43,  devised  by  Lodge  and  Muirhead.  It 
consists  of  a  slowly  moving  steel  disk  a  whose  sharpened  edge  is 
prevented  from  coming  into  contact  with  the  small  globule  of  mer- 
cury 6  by  means  of  a  thin  film  of  oil  interposed  between  the 
mercury  and  the  steel  and  contained  in  the  recess  d.  Oscillations 
passing  through  the  oil  cause  a  breakdown  of  its  high  resistance, 


58 


RADIOTELEGRAPHIC  APPARATUS  59 

permitting  a  translating  device  to  operate  by  reason  of  the  improved 
conductivity.  Upon  cessation  of  the  oscillations,  the  movement  of 
the  disk  re-establishes  the  initial  receptivity. 

Italian  Navy  Coherer: — The  Marconi  Company  used  with  suc- 
cess for  a  time  the  so-called  "auto-coherer"  invented  by  Signor 
Castelli,  and  often  referred  to  as  the  Italian  Navy  coherer.  The 


c' 


Fig.  44.     Castello  "Auto-Coherer" 

action  is  entirely  automatic.  In  Fig.  44,  z  is  an  iron  cylinder  separa- 
ting two  globules  of  mercury;  c  and  c'  are  of  carbon.  Cohesion 
between  the  mercury  globules  and  electrodes  exists  only  under  the 
stimulus  of  the  oscillations. 

Tantalum-Mercury  Coherer: — The  tantalum-mercury  imperfect- 
contact  detector  invented  by  L.  H.  Walter  is  the  simplest  as  well  as 
one  of  the  best  of  the  self-restoring  coherers.  A  small  portion  of  the 
filament  of  a  tantalum  incandescent  lamp  is  connected  to  a  piece  of 
platinum  wire  for  terminal  purposes,  and  the  tip  of  the  tantalum  is 
immersed  in  mercury,  which  thus  forms  the  other  terminal.  The 
whole  may  be  sealed  up  in  a  vacuum  to  avoid  oxidization  of  the 
mercury.  The  contact  offers  very  high  resistance  to  a  small  e.  m.  f., 
but  falls  very  low  under  the  influence  of  the  received  oscillations. 
It  is  rapidly  self-restoring.  Telephone  receivers  are  often  used  with 
this  class  of  detector  instead  of  the  Morse  relay  and  recorder,  thus 
allowing  the  detection  of  signals  from  much  greater  distances  owing 
to  the  extreme  sensitiveness  of  the  Bell  instrument  to  minute  differ- 
ences of  current.  Such  a  receiver  responds  by  a  buzz  to  the  Morse 
dash  from  the  distant  station. 

Valve,  or  Rectifier,  Detectors.  One  of  the  difficulties  of  de- 
tecting electric  oscillations  is  the  fact  that  they  are  of  an  alternating 
nature.  With  the  present  means  at  our  disposal  it  cannot  be  said 
that  we  can  detect  the  presence  of  minute  alternating  currents  with 
the  ease  with  which  we  can  detect  direct  currents  of  equal  value. 
This  has  led  to  endeavors  to  rectify  the  high-frequency  alternations 
of  the  received  oscillations.  Detectors  of  this  type  are  known  as 
valve,  or  rectifier,  detectors,  and  one  of  the  simplest  means  of  detect- 
ing radiotelegraphic  signals  is  afforded  by  such  devices.  To  their 


59 


60 


WIRELESS  TELEGRAPHY 


extreme  simplicity  is  due  to  a  large  extent  the  present  number  of 
amateur  wireless  installations  to  be  seen  on  all  sides.  The  action 
of  the  silicon  detector,  shown  in  Fig.  45,  is  due  to  the  fact  that  a  con- 
siderable number  of  substances  in  nature  possess  the  property  of 
unilateral  conductivity,  or  the  property  of  conducting  electricity 
freely  in  only  one  direction.  H.  H.  C.  Dunwoody  discovered  that 
carborundum  possessed  this  property  to  a  very  marked  degree,  and 
would  act  as  a  detector  if  introduced  into  a  receiving  circuit  in  place 
of  a  filings  coherer.  He  later  observed  that  no  battery  was  necessary 

when  using  a  telephone  receiver 
shunted  by  a  small  condenser, 
as  shown  in  Fig.  46.  The  fol- 
lowing substances  will  all  act  in 
place  of  the  carborundum:  cop- 
per pyrites,  iron  pyrites,  galena, 
silicon,  zinc  oxide  (perikon),  mol- 
ybdenum sulphide,  and  titanium 
oxide.  G.  W.  Pierce  has  found 
that  the  resistance  of  these  sub- 
stances may  be  3,000  times 
greater  in  one  direction  than  in 
the  other.  The  theory  of  this 
peculiar  action  cannot  as  yet  be 
said  to  be  complete. 

Carborundum,  silicon,  and 
perikon  seem  to  be  the  most  satis- 
factory, particularly  silicon,  which 

makes  a  very  sensitive  and  inexpensive  device.  Such  materials  used 
as  detectors  of  electric  waves  allow  but  one-half  of  each  wave  to  pass, 
thus  giving  rise  in  the  telephone  to  a  rapidly  pulsating  current  in 
one  direction  to  which  the  telephone  can  respond.  The  energy  of  the 
oscillations,  therefore,  directly  achieves  the  audible  signal.  It  has 
been  found,  however,  that  in  some  cases  better  results  are  obtained 
with  a  shunted  battery  cell  in  the  circuit.  It  is  important  when  using 
any  form  of  valve  detector  that  excellent  connection  with  the  crystal 
should  be  maintained  at  least  on  one  terminal,  a  deposit  of  some  suit- 
able metal  often  being  employed,  thus  permitting  of  a  large  area  of 
contact.  The  adjustable  contact  is  preferably  pointed  and  securely  held. 


Fig.  45.     Silicon  Detector 


60 


RADIOTELEGRAPHIC  APPARATUS 


61 


AZfflAL 


Glow-Larnp  Detector: — The  glow-lamp  detector,  invented  by 
Prof.  J.  A.  Fleming,  was  one  of  the  first  valve  detectors.  The  theory 
of  its  operation  may  be  understood  from  the  inventor's  description 
and  with  reference  to  Fig.  47.  "An  ordi- 
nary incandescent  lamp  with  carbon  fila- 
ment has  a  metal  plate  included  in  the 
glass  bulb,  or  a  metal  cylinder  C  placed 
round  the  filament,  the  said  plate  or 
cylinder  being  attached  to  an  indepen- 
dent insulated  platinum  wire  T  sealed 
through  the  glass.  When  the  carbon 
is  rendered  incandescent  by  electric 
current,  the  space  between  the  filament 
and  the  plate,  occupied  by  a  highly 
rarefied  gas,  possesses  a  unilateral  con- 
ductivity, and  negative  electricity  will 
pass  from  the  incandescent  filament  to 
the  plate,  but  not  in  the  opposite 
direction.  This  effect  depends  upon  the 
well-known  fact  that  carbon  in  a  state 
of  high  incandescence  liberates  electrons 

or  negative  ions;  that  is  to  say,  point  charges  of  negative  electricity. 
These  electrons,  or  corpuscles,  are  constituents  of  the  chemical 
atom.  Hence  a  carbon  filament  in  an  incandes- 
cent lamp  is  discharging  from  its  surface  nega- 
tive electricity,  which  may  even  amount  to  as 
much  as  an  ampere  or  even  several  amperes  per 
square  centimeter.  If,  then,  an  incandescent 
lamp  made  as  described  has  its  filament  rendered 
incandescent  by  a  continuous  current,  and  if 
another  .circuit  is  formed  outside  the  lamp  con- 
necting the  negative  terminal  of  the  filament 
with  the  insulated  metal  plate  or  cylinder  in  the 
bulb,  and  if  oscillations  are  set  up  in  this  circuit, 
negative  electricity  will  be  able  to  move  through 
this  circuit  from  the  filament  to  the  plate  inside  the  bulb,  but  not 
in  the  opposite  direction." 

It  is  evident  from  the  foregoing  that  there  are  present  in  the 


FAffTH 


Fig.  46.    Diagram  of  Dun 
woody  Detector 


Fig.  47.    Fleming 
Glow-Lamp  Detector 


61 


62 


WIRELESS  TELEGRAPHY 


glow-lamp  device  the  essentials  of  a  valve  detector.  Fig.  48  shows 
a  receiver  circuit  employed  by  Marconi  making  use  of  the  Fleming 

lamp.  Instead  of  passing  the 
rectified  uni-directional  impulses 
directly  through  the  telephone, 
they  are  passed  around  the 
secondary  of  a  large  induction 
coil  in  series  with  a  condenser,  to 
the  primary  of  which  the  tele- 
phone receiver  is  connected. 
Prof.  Fleming  is  authority  for 
the  statement  that  this  arrange- 
ment, when  suitably  adjusted,  is 
"one  of  the  best  long-distance 
receivers  for  electric  waves  yet 
devised." 

Audion: — The  so-called  au- 
Fig.  48.    Marconi  circuit  Using         dion  of  DeForest  is  a  modifica- 

Fleming  Detector  . 

tion  oi  the  r  leming  detector  just 

described.  Fig.  49  shows  its  connection  [n  a  receiving  circuit.  The 
lamp  used  has  a  low- voltage  tantalum  filament  with  two  wings,  or 
terminals,  sealed  in  the  bulb,  as  shown.  This  detector  is  said  to 
be  fairly  sensitive,  though  of  short  life. 

Magnetic  Detectors.    During  the  summer  of  1902,  Marconi  was 
successful  in  receiving  signals  sent  out  from  Poldhu  on  the  coast  of 

Cornwall  to  Flace  Bay,  Nova 
Scotia,  by  means  of  a  re- 
markably ingenious  magnetic 
receiving  device  invented  by 
himself  and  called  a  magnetic 
detector.  Since  that  time 
many  devices  have  been  pat- 
ented depending  for  their  op- 
eration upon  the  magnetic 

Fig.  49.  Receiving  Circuit  with  Audion  Detector      effeCtS  °f  the  electric  OScilla- 

tions.    There  has  been  much 

discussion  relative  to  the  action  involved  in  the  Marconi  device  as 
well  as  in  other  modifications  based  on  the  magnetic  phenomena 


62 


RADIOTELEGRAPHIC  APPARATUS 


63 


associated  with  oscillatory  currents.  The  explanation  advanced  by 
Marconi  himself  will,  therefore,  be  given  here,  which  in  substance 
is  as  follows,  reference  being  made  to  Fig.  50. 

The  aerial  and  ground  are  connected  to  a  few  turns  of  rather 
heavy  wire  wound  upon  a  glass  tube  T  over  which,  but  insulated 
from  it,  is  another  coil  inductively  related  to  the  first  and  connected 
to  the  terminals  of  a  telephone  receiver.  Two  strong  permanent 
magnets  are  placed  with  like  poles  together,  as  indicated.  P  and  P' 
are  two  pulleys  carrying  on  their  periphery  an  endless  belt  composed 
of  several  fine  wires  of  about  No.  36  gauge,  which  are  made  to  pass 


Fig.  50.     Diagram  of  Marconi  Magnetic  Detector 

continually  through  the  axis  of  the  coils  by  a  train  of  gears  not  shown. 
Owing  to  the  hysteresis  of  the  material  of  the  band  it  tends  to  retain 
its  magnetism  for  a  short  period  after  it  has  passed  out  of  the  strongest 
part  of  the  field;  but  if  a  train  of  waves  from  the  aerial  is  passed 
through  the  primary  coil  to  the  ground,  the  effect  is  to  annul  the 
hysteresis  and  thereby  to  hasten  the  demagnetization  of  the  iron 
wire.  This  action  results  in  a  variation  of  the  flux  in  the  secondary 
winding,  thus  inducing  electromotive  forces  in  the  secondary  coil, 
which  make  themselves  audible  in  the  telephone  as  a  series  of  sharp 
ticks.  This  is  said  to  be  one  of  the  most  sensitive  devices  ever 
made. 

A  diagrammatic  drawing  of  a  magnetic  detector,  invented  by 
H.  Shoemaker,  which  very  closely  resembles  the  early  embodiment  of 


63 


64 


WIRELESS  TELEGRAPHY 


the  Marconi  apparatus  is  shown  in  Fig.  51.  There  have  been  many 
variations  of  the  magnetic  detector  but  space  will  not  permit  of  a 
description  of  less  important  forms. 

Thermo-electric  Detectors.  Comprehended  under  the  head  oi 
thermo-electric  detectors  are  those  instruments  which  depend  for 
their  action  on  the  heating  effects  of  the  oscillatory  currents.  These 


Fig.  51.     Shoemaker  Magnetic  Detector 


detectors  are  especially  useful  in  making  quantitative  measurements 
of  the  amount  of  energy  received  under  a  given  condition,  and  indeed 
find  their  greatest  utility  therein.  Fessenden  has  given  great  care  to 
his  investigations  of  this  form  of  detector  with  the  result  that  his 
so-called  "barreter"  shown  in  Fig.  52  is  of  the  same  order  of  sensitive- 
ness as  the  coherer.  It  consists  of  a  short  piece 
of  exquisitely  fine  platinum  wire  connected  to 
suitable  terminal  wires  and  the  whole  enclosed 
in  a  vacuum  bulb.  The  temperature  rises  rap- 
idly under  the  action  of  the  oscillations,  causing 
an  increase  in  resistance  which  is  indicated  by  a 
Wheatstone  bridge,  in  the  circuit  of  which  the 
detector  is  connected  as  one  of  the  arms.  At- 
tempts have  been  made  to  apply  the  phenomena 
of  the  thermo  couple  in  this  connection,  but  with 
only  qualified  success.  It  would  seem  for  many  reasons  that  thermo- 
electrical  detectors  will  not  be  able  to  compete  with  other  forms  in 
long-distance  work. 


Fier.  52.     Fessenden 
Barreter 


64 


RADIOTELEGRAPHIC  APPARATUS 


65 


Fig.  53.     Liquid  Barreter 


Electrolytic  Detectors.  It  remains  to  take  up  the  class  of  de- 
tectors known  as  electrolytic.  DeForest's  name  is  associated  with 
this  variety  of  receiving  device,  as  it  was  first  extensively  used  by 
him  in  a  form  invented  by  himself.  It  consists  of  a  glass  tube  \  inch 
in  diameter  enclosing  conductor  plugs 
after  the  manner  of  the  Branly  coherer. 
In  the  interspace  is  placed  a  paste  com- 
posed of  rather  coarse  filings  worked  up 
with  an  equal  quantity  of  oxide  of  lead 
in  glycerine  or  vaseline  with  a  trace  of 
water  or  alcohol.  Its  resistance  in- 
creases during  the  passage  of  the  wave 
train. 

Fessenden  Liquid  Barreter: — The 
most  sensitive  and  practical  electrolytic 
detector  is  the  liquid  barreter  invented 
by  Fessenden,  Fig.  53.  It  consists  essen- 
tially of  a  small  containing  vessel  filled  with  nitric  acid  into  which 
projects  a  platinum  wire  electrode,  which  is  of  extremely  small  diam- 
eter. The  apparent  resistance  of  the  cell  is  greatly  reduced  by  the 
oscillations.  The  exact  nature  of  the  action  is  not  agreed  upon  by 
investigators.  It  was  with  a  refined  form  of  this  detector  that  trans- 
Atlantic  signals  were  first  received  from  Scotland  by  the  National 
Electric  Company  at  Brant  Rock,  Massachusetts. 

Hozier-Brown  Detector: — The  Hozier-Brown  system  of  wire- 
less telegraphy  employs  a  detector  classified  by  some  as  depending 
on  imperfect  contact,  but  by  others  as 
being  electrolytic  in  its  action.  It  con- 
sists of  a  small  portion  of  peroxide  of 
lead  held  between  terminals  of  lead  and 
platinum,  Fig.  54.  The  lead  terminal 
is  much  smaller  than  the  other,  being  a 
blunt  point  rendered  adjustable  by  a 

knurled   screw.     A  two-volt  accumulator      Fig-  54-     Hosier-Brown  Detector 

connected  in  series  gives  the  best  results,  according  to  the  inventor. 

Electrodynamic  Detectors.     Mention  might  be  given  in  passing 

to  the  electrodynamic  detector  devised  by  Fessenden,  although  it 

has  never  been  used  extensively.     It  is  designed  to  operate  on  the 


65 


66  WIRELESS  TELEGRAPHY 

principle  that  a  metallic  disk,  suspended  in  a  circular  coil  through 
which  an  alternating  current  is  flowing,  and  at  an  angle  of  45  degrees 
to  the  plane  of  winding  of  the  coil,  tends  to  turn  so  as  to  take  up  a 
position  at  right  angles  to  the  plane  of  the  coil.  This  was  a  fact 
discovered  independently  by  Elihu  Thomson  and  J.  A.  Fleming. 
Fessenden  used  an  extremely  light  disk  hung  by  a  quartz  fiber,  and 
he  succeeded  in  obtaining  marked  deflections  of  a  beam  of  light 
reflected  from  a  small  mirror  fastened  to  the  disk.  This  device, 
like  the  thermo-detector,  has  been  of  great  service  in  making  quan- 
titative measurements  of  oscillatory  currents. 

Auxiliary  Apparatus.  It  would  be  beyond  the  scope  of  the 
present  work  to  give  ?n  extended  discussion  of  the  various  small 
devices  used  in  connection  with  the  local  receiving  circuits,  as  many 
of  the  instruments  are  not  in  any  way  peculiar  to  radiotelegraphy, 
being  the  common  adjuncts  of  wire  telegraphy.  Mention  will  only 
be  given  to  a  few  points  of  importance  wherein  such  appliances  differ 
from  those  commonly  employed. 

The  relay  supplied  by  makers  of  telegraphic  instruments  is 
usually  wound  with  an  insufficient  number  of  turns  to  be  efficiently 
used  in  connection  with  a  coherer  and  local  battery  as  a  means  of 
actuating  a  Morse  recorder.  Rewinding  is,  therefore,  often  resorted 
to.  Polarized  relays  are  found  to  be  the  best  suited  to  this  class  of 
work  and  should  be  wound  to  a  very  high  resistance  in  connection  with 
all  potentially  operable  detectors.  No.  40  wire  is  often  employed. 

Sparking  at  the  contacts  of  the  relay  is  often  prevented  by  the 
employment  of  four  or  five  so-called  "polarized"  cells  shunted  across 
the  contacts.  They  are  made  by  inserting  a  pair  of  platinum  wires 
through  the  cover  of  a  small  containing  vessel  partly  filled  with  dilute 
sulphuric  acid,  allowing  the  solution  to  cover  the  ends  of  the  electrodes 
thus  formed. 

The  telephone  receivers  for  use  with  many  forms  of  detector 
are  much  more  efficient  if  wound  to  a  higher  resistance  than  is  neces- 
sary in  the  common  commercial  instrument.  Receivers  are  manu- 
factured in  a  great  variety  of  forms,  only  differing  from  one  another 
in  some  slight  structural  modification.  The  kind  known  as  operator's 
double-head  receivers  of  the  watch-case  design  wound  to  a  resistance 
of  about  500  or  1,000  ohms  are  well  adapted  to  the  requirements  of 
radiotelegraphy. 


66 


RADIOTELEGRAPHIC  APPARATUS  67 

Dry  cells  developing  an  electromotive  force,  when  fresh,  of  about 
1.5  volts  are  generally  used  in  the  local  recorder  and  tapper  circuits. 
One  such  cell  is  frequently  used  in  the  relay  and  the  coherer  circuit. 

Measuring  Instruments.  Perhaps  in  no  department  of  electro- 
technics  are  the  quantitative  values  of  the  electrical  measurements 
of  more  vital  importance  than  in  the  science  of  radiotelegraphy. 
A  well-equipped  station,  therefore,  possesses  efficient  instruments 
for  the  measurement  of  the  various  electrical  factors  involved.  Be- 
sides the  common  appliances  of  this  nature,  such  as  the  voltmeter, 
ammeter,  Wheats  tone  bridge,  etc.,  it  is  highly  advisable  to  have  the 
requisite  means  for  making  accurate  determinations  of  capacity  and 
inductance.  Wave-lengths  can  be  measured  by  wave-meters,  or 
cymometers.  These  devices  are  now  on  the  market  and  are  of  great 
utility  in  a  wireless  station. 


67 


CHAPTER  V 
SYSTEMS  OF  RADIOTELEGRAPHY 

The  history  of  radiotelegraphy  repeats  once  more  the  old  story 
that  is  so  often  connected  with  great  inventions.  The  world  being 
possessed  of  a  new  scientific  principle,  many  minds  in  many  parts 
of  the  world  are  simultaneously  bent  upon  its  practical  application, 
with  the  result  that  the  fundamental  principle  finds  embodiment  in 
various  methods  of  accomplishing  a  similar  purpose.  The  startling 
nature  of  the  discovery  of  electric  waves  was  bound  to  give  rise  to 
unprecedented  activity  in  the  field  of  experimental  investigation; 
and  such  experiments  as  were  particularly  successful  were  bound  to 
prompt  investigators  to  seek  patent  protection  on  their  modifications; 
and  this  in  turn  gave  rise  to  numberless  "systems"  of  radiotelegraphy. 

A  voluminous  list  of  names  could  be  given  of  those  who  have 
contributed  to  the  advancement  of  radiotelegraphy  in  regard  to  both 
theory  and  practice.  Among  the  best-known  American  investigators 
are  Fessenden,  DeForest,  Clark,  Stone,  and  Massie.  Each  of  these 
men  has  devised  a  system  which  bears  his  name.  In  England  the 
work  has  been  carried  on  by  men  of  such  unqualified  distinction  as 
Lodge,  Alexander  Muirhead,  Fleming,  Thomson,  and  Rutherford. 
Slaby,  Arco,  and  Braun  are  the  names  best  known  in  Germany.  The 
French  are  represented  by  Ducretet,  Branly,  Rochefort,  and  Tissot, 
besides  other  men  of  lesser  fame.  We  have  seen  how  largely  Italy 
has  contributed  to  the  subject;  besides  Marconi  and  Righi,  mention 
should  be  made  of  Solari,  Castelli,  and  Tommasina.  Baviera  in 
Spain,  Popoif  in  Russia,  Schafer  in  Austria,  Guarini  in  Belgium,  and 
Ricaldoni  in  the  Argentine  Republic  have  all  invented  systems  which 
have  been  more  or  less  used  in  their  respective  countries.  The 
Japanese  have  also  devised  a  system  that  successfully  stood  the  test 
of  service  in  the  Russo-Japanese  war. 

The  development  of  the  art  in  the  various  countries  has  been 
carried  on  largely  by  representative  investigators,  and  in  many  in- 


68 


SYSTEMS  OF  RADIOTELEGRAPHY  69 

stances  the  governments  have  adopted  a  system  exploited  by  their 
subjects.  The  United  States  government,  however,  has  purchased 
and  experimented  with  most  of  the  prominent  systems  offered,  and 
as  a  result  the  army  and  navy  equipments  comprehend  quite  a  variety 
of  apparatus  of  different  makes. 

Telegraphic  Codes.  Before  beginning  the  description  of  the 
more  important  systems  of  radiotelegraphy  in  use  at  the  present  time, 
we  will  consider  the  telegraphic  codes  employed  in  wireless  corre- 
spondence. There  are  three  alphabetical  codes  commonly  used  at 
the  present  time,  viz,  the  Continental,  the  Morse,  and  the  Navy 


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Fig.  55.     Continental  Code 

codes.  By  far  the  greatest  amount  of  business  is  carried  on  in  the 
Continental  code,  especially  between  ships  and  shore  stations.  The 
Morse  is  more  commonly  employed  for  overland  service,  while  the 
Navy  code  is  confined  to  naval  purposes.  Abbreviations  of  the  com- 
moner words  are  often  made  use  of  in  transacting  the  ordinary  run 
of  business.  The  three  codes  are  shown  in  Figs.  55,  56,  and  57. 
Marconi  System.  A  detailed  description  has  already  been  given 
of  the  Marconi  system  as  it  was  about  the  year  1900.  Since  then  the 
system  has  been  developed  to  a  remarkable  degree  so  that  it  stands 
today  a  commercial  factor  of  large  pretensions.  The  Marconi 


69 


70 


WIRELESS  TELEGRAPHY 


stations  are  scattered  in  many  parts  of  the  globe  and  are  operated 
in  conjunction  with  all  the  large  telegraph  and  cable  companies. 


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Fig.  56.    Morse  Code 

In  addition  to  the  numerous  land  stations  a  very  large  number  of 
vessels   are   equipped   with   the  Marconi  apparatus,  including   the 


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Fig.  57.     Navy  Code 

ocean  liners  of  nearly  all  the  large  steamship  companies,  such  as  the 
Cunard  line,  the  Hamburg-American  line,  the  Norddeutscher  Lloyd, 


70 


SYSTEMS  OF  RADIOTELEGRAPHY 


71 


and  many  other  lines  too  numerous  to  mention.    Three  stations  are 
in  operation  in   China. 

For  short-distance  equipment  to  be  used  over  a  few  hundred 
miles,  such,  for  instance,  as  is  usually  installed  on  Atlantic  liners, 
the  Marconi  Company  employs  an  induction  coil  with  mechanical 
break  to  charge  a  battery  of  six  to  twelve  Leyden  jars.  Two  coils 
and  two  sets  of  jars  are  often  supplied  in  order  to  readily  produce 
two  different  wave-lengths.  A  single  spark  gap  is  now  used.  The 
Marconi  magnetic  detector  is  generally  employed,  owing  to  its  great 
simplicity  and  ease  of  adjustment.  An  important  improvement 
evolved  by  the  meeting  of  practical  difficulties  is  known  as  the  X- 
stopper,  X  being  the  name  given  to  certain  irregular  atmospheric 
disturbances  of  an  electromagnetic  nature  which  manifest  them- 


Fig.  58.    Complete  Marconi  Sending  and  Receiving  Circuit 

selves  as  stray  signals  of  sufficient  energy  to  cause  confusion  in  the 
reception  of  messages.  The  means  devised  by  Marconi  for  over- 
coming these  objectionable  interruptions  may  be  seen  in  diagram 
in  Fig.  58,  which  shows  one  form  of  the  complete  sending  and  receiv- 
ing circuits  employed  by  the  Marconi  Company.  The  lower  end 
of  the  receiving  aerial  is  connected  with  a  plurality  of  adjustable 
oscillatory  circuits  of  varying  periodicity  which  terminate  in  the 
primary  oscillation  circuit  of  the  receiving  device.  The  operation 
of  the  contrivance  depends  upon  the  ability  of  the  first  three  grounded 
circuits  to  perform  the  function  of  leading  to  the  ground  waves  whose 
frequency  does  not  accord  with  the  periodicity  of  the  system  as  a 
whole.  It  will  be  noted  that  the  closed  type  of-  oscillatory  circuit 


71 


72  WIRELESS  TELEGRAPHY 

inductively  coupled  to  the  aerial  as  before  described  is  used  in  the 
transmitting  arrangement  of  apparatus.  The  later  form  of  oscilla- 
tion transformer  used  at  the  sending  station  is  designed  to  provide 
means  for  varying  the  closeness  of  the  inductive  couple.  This 
possesses  many  advantages. 

The  Marconi  Company  has  equipped  several  high-power  trans- 
Atlantic  stations.  The  modifications  of  the  short-distance  apparatus 
made  necessary  for  long-distance  signaling  pertain  largely  to  means 
for  controlling  a  much  larger  amount  of  energy  at  the  transmitting 
station  and  the  employment  of  longer  wave-lengths.  Communica- 
tion was  established  the  latter  part  of  1907  between  Cape  Breton, 
Nova  Scotia,  and  Clifden,  Ireland,  by  waves  12,000  feet  in  length 
generated  by  means  of  the  Marconi  high-speed  disk  discharger  used 
in  conjunction  with  a  condenser  of  1.16  microfarads  charged  to  80,000 
volts.  Horizontal,  or  directive,  antennae  are  used  with  their  free 
ends  directed  away  from  each  other  at  the  two  stations,  the  hori- 
zontal portion  being  about  1,000  feet  long  and  raised  about  200  feet 
in  the  air.  The  Marconi  magnetic  detector,  and  also  a  modification 
of  the  Fleming  glow-lamp  detector,  have  been  used  as  receptors  in 
this  class  of  work.  fc 

An  ingenious  form  of  signaling  key  for  use  in  connection  with 
high-power  installations  employing  alternating  current  has  been 
patented  by  the  I  Marconi  Company.  The  fundamental  feature  of 
the  invention  consists  in  the  use  of  a  laminated  electromagnet 
through  which  the  current  to  be  broken  is  conducted,  so  placed 
as  to  hold  the  key  closed  by  the  attraction  of  an  armature  on  the 
key  until  the  current  reaches  the  zero  value,  at  which  time  the  key 
is  allowed  to  break  connection  unaccompanied  by  a  spark.  The 
connection  may  be  made  and  maintained  at  will,  but  upon  release 
of  the  key  the  circuit  is  broken  at  the  instant  when  the  current  reaches 
the  zero  value;  the  frequency  of  the  alternating  current  being  at  least 
such  that  this  occurs  about  100  times  per  second,  the  maximum  lag 
of  the  key  behind  the  movement  of  the  operator's  button  is  inap- 
preciable. 

Fessenden  System.  Fessenden  undoubtedly  holds  a  position 
of  first  rank  among  scientific  investigators  in  the  field  of  electric 
radiation.  Moreover,  he  has  proven?,  himself  to  be  an  inventor  of 
exceptional  originality.  His  experiments  in  ladiotelegraphy  date 


72 


SYSTEMS  OF  RADIOTELEGRAPHY  73 

back  to  the  early  days  of  the  art.  The  National  Electric  Signaling 
Company  now  control  the  long  list  of  patents  resulting  from  his 
researches  beginning  in  1897  and  covering  a  great  variety  of  subjects 
pertaining  to  every  part  of  radiotelegraphic  equipment  as  well  as  to 
radiotelephony. 

The  National  Electric  Signaling  Company  completed  in  1905 
two  trans-Atlantic  stations  for  communication  between  Brant  Rock, 
Massachusetts,  and  Machrihanish,  Kintyre,  Scotland,  a  distance  of 
more  than  3,000  miles.  Successful  communication  was  established  on 
Jan.  3rd,  1906,  the  detector  used  being  the  liquid  barreter,  already 
described.  An  interesting  feature  of  these  long-distance  stations  is 
the  design  of  the  aerial.  This  is  in  the  form  of  a  vertical  steel  tube 
3  feet  in  diameter  and  415  feet  long,  resting  upon  an  insulated  foun- 
dation, and  supporting  an  "umbrella"  formed  of  wires  at  the  top. 
This  structure  is  held  in  an  erect  position  by  sixteen  guys  insulated 
to  withstand  a  voltage  of  over  150,000.  A  25-kilowatt,  60-cycle,  boiler- 
engine  alternator  supplies  the  energy. 

Fessenden  has  devoted  much  time  to  the  problems  of  selection, 
interference,  and  tuning.  As  a  result  of  his  labors  in  this  field,  the 
Fessenden  system  may  be  said  to  represent  the  highest  development 
in  this  respect  yet  achieved. 

The  National  Electric  signaling  equipment  comprises  a  transmit- 
ting device  of  the  direct-coupled  aerial  variety,  characterized  by  the 
arrangement  of  the  sending  key  which,  by  cutting  out  a  certain 
amount  of  inductance  in  the  oscillatory  circuit,  alters  the  frequency  of  the 
waves  emitted — instead  of  interrupting  the  primary  circuit  and  caus- 
ing a  cessation  of  the  waves,  as  in  common  practice.  This  requires 
that  a  receiving  station  be  tuned  with  great  accuracy,  in  order  to 
respond  to  a  slight  difference  of  wave-length  only,  an  untuned  cir- 
cuit being  thus  unable  to  receive  any  signals  other  than  a  continu- 
ous dash.  It  is  claimed  that  a  difference  of  wave-length  occasioned 
by  the  operation  of  the  key,  amounting  to  less  than  one  per  cent  is 
sufficient  to  achieve  perfect  communication.  This  exceptional  free- 
dom from  interference  is  due  largely  to  the  employment  of  what  is 
called  an  interference  preventer,  diagrammatically  represented  in 
Fig.  59,  which  shows  an  improved  Fessenden  receiving  circuit.  The 
aerial  is  connected  through  a  variable  inductance  to  a  divided  circuit 
and  thence  to  the  ground.  In  each  half  of  the  divided  circuit  is 


73 


74 


WIRELESS  TELEGRAPHY 


placed  a  condenser  in  series  with  the  primary  of  an  air-core  oscilla- 
tion transformer.  The  secondary  terminals  of  the  transformer  are 
united  by  a  condenser  A,  a  signal  translating  device  consisting 
of  the  liquid  barreter  B,  a  potentiometer  C,  and  a  telephone  receiver 
D— all  in  series.  The  secondary  terminals  of  the  transformers  are 
connected  up  so  as  to  oppose  each  other,  after  the  manner  of  a  Hughes 

induction  balance.  The  aerial 
and  one-half  of  the  divided  cir- 
cuit are  tuned  to  the  desired 
frequency,  the  other  half  being 
momentarily  disconnected;  then 
the  latter  is  connected  again  and 
the  capacity  of  the  condenser 
E  is  adjusted  until  the  disturb- 
ing signals  are  eradicated.  The 
operation  is  theoretically  as  fol- 
lows: Signals  of  the  proper 
wave-length  pass  almost  entirely 
through  the  side  of  the  divided 
circin't  which  is  tuned  to  corre- 
spond, while  waves  of  any  other 
frequency  pass  with  equal  ease 
through  both  sides  of  the  di- 
vided circuit,  thereby  acting  dif- 
ferentially on  the  secondary  os- 
cillation circuit  because  the  sec- 
ondary windings  of  the  oscilla- 
tion transformers  oppose  each 
other.  It  is  said  that  this  arrangement  will  differentiate  between 
waves  differing  but  one  per  cent  in  wave-length. 

Fessenden  apparatus  is  sometimes  supplied  with  a  so-called 
intensity  regulator  for  modifying  the  intensity  of  radiation  without 
affecting  the  frequency.  This  is  for  use  in  communicating  with 
nearby  stations. 

Telefunken  System.  The  system  designated  by  this  title  is  the 
result  of  an  amalgamation  of  two  formerly  separate  systems  of 
radiotelegraphy.  After  patent  litigation  in  the  German  courts,  die 
Gesellschaft  fur  Drahtlose  Telegraphic  (Wireless  Telegraph  Co.)  of 


Fig.  59.     Fessenden  Interference  Preventer 


74 


SYSTEMS  OF  RADIOTELEGRAPHY 


75 


Berlin  was  formed  to  take  over  the  conflicting  interests  represented 
by  the  Slaby-Arco  system  and  the  Braun-Siemens-Halske  system. 
This  company  is  operating  under  patents  granted  to  Dr.  Rudolph 
Slaby  of  Berlin,  Count  Georg  von  Arco,  and  Prof.  Ferdinand  Braun 
of  the  University  of  Strasburg,  each  of  whom  has  made  important 
contributions  to  the  subject  of  space  telegraphy.  The  Telefunken 
system  has  been  developed  to  a  remarkable  degree,  due  largely  no 
doubt  to  the  powerful  influence  of  the  German  government,  and 
possesses  stations  all  over  the  world — numbering  more  than  500. 


Fig.  60.     Circuit  Diagram,  Telefunken  System 

Their  equipment  is  sold  outright  and  is  noted  for  excellence  of  work- 
manship. The  earlier  sets  of  apparatus  were  furnished  with  a  Morse 
recorder  operated  by  a  coherer  of  the  nickel  filings  type,  but  latterly 
an  electrolytic  detector  and  head  telephone  are  furnished  as  a  means 
of  reception.  As  the  recorder  and  associated  apparatus  cut  down 
the  speed  of  signaling  to  a  degree  that  seriously  impairs  their  value 
for  commercial  work,  the  employment  of  the  telephone  is  becoming 
almost  universal  practice.  The  recording  mechanism  is,  however, 
preferred  by  many  naval  authorities  over  the  telephone,  as  it  eliminates 
the  personal  equation  of  the  operator  and  leaves  no  possibility  of 
error  in  the  received  messages. 

A  complete  wiring  diagram  of  the  connections  of  the  Telefunken 
system  is  shown  in  Fig.  60.    The  aerial  is  coupled  directly  onto  the 


76 


WIRELESS  TELEGRAPHY 


AEfl/AL 


closed  oscillatory  circuit.  A  small  air  gap,  or  cut-out,  is  located  in 
the  transmitting  aerial  to  prevent  the  received  oscillations  from  flow- 
ing through  the  transmitting  circuits.  Such  a  gap  offers  no  hin- 
drance to  the  high-potential  oscillations  surging  through  the  radiating 
circuit  of  the  antennae.  Means  is  shown  for  adjusting  the  inductance 
in  the  closed  circuit  of  the  transmitter,  and  the  inductance  between 
this  circuit  and  the  earth. 

The  Telefunken   Company  has   more  recently  announced  the 
so-called  singing-spark  system  of  radiotelegraphy,  which  is  based 

on  the  discovery  of  Wein  that 
exceedingly  powerful  discharges, 
possessing  useful  properties  for 
radiotelegraphy,  may  be  ob- 
tained from  very  short  spark 
gaps.  The  air  gap  in  this  new 
modification  of  the  Telefunken 
system  is  divided  between  a 
plurality  of  copper  or  silver 
disks  kept  apart  by  rings  of 
mica*  This  form  of  oscillation 
generator  is  called  by  the  Ger- 
man firm  a  quenched  spark. 
When  in  operation  the  device 
gives  forth  a  clear  musical  tone, 
which  gives  the  system  its  name. 
The  detector  employed  is  of 
special  design  and  said  to  be 
more  sensitive  than  the  electro- 
lytic type.  It  is  claimed  for 
the  singing-spark  system  that  shorter  aerials  may  be  used  and  that  a 
greater  percentage  of  the  energy  of  the  source  can  be  rendered  avail- 
able for  radiation;  also  that  the  tuning  of  stations  is  greatly  facilitated. 
Von  Lepel  System.  It  has  been  claimed  by  the  German  ex- 
perimenter, Von  Lepel,  that  he  applied  the  discovery  of  Wein  to 
practical  radiotelegraphy  prior  to  its  adoption  by  the  Telefunken 
people.  However  this  may  be,  the  discovery  referred  to  seems  to  be 
of  importance,  and  though  this  method  of  producing  oscillations  is 
still  in  the  experimental  stage,  the  system  of  Von  Lepel  based  thereon 


Fig.  61.     Von  Lepel  Oscillation  Generator 
Circuit 


76 


SYSTEMS  OF  RADIOTELEGRAPHY 


77 


is  of  interest.  The  oscillation  generator  designed  by  him  is  shown 
in  Fig.  61.  It  consists  essentially  of  two  copper-box,  air-cooled 
electrodes  about  5  inches  in  diameter,  separated  by  a  thin  (.002  inch) 
disk  of  paper  with  a  J-inch  hole,  in  the  center  for  the  spark.  The 
paper  serves  to  keep  the  arc  from  running  out  to  the  edge  of  the 
electrodes.  This  paper  constantly  burns  away,  but  a  piece  will 
last  about  three  hours.  The  connections  are  indicated  in  the  dia- 
gram, which  shows  a  direct-current  generator,  but  an  alternating 
current  will  also  operate  the  device.  L  and  L'  are  inductively  coupled 
inductances,  the  value  of  U  being  very  small.  The  capacity  in  series 
with  U  and  bridged  across  the  gap  is  also  very  small.  A  satisfactory 
explanation  accounting  for  the  effects  obtained  has  not  yet  been  put 
forth.  Tests  thus  far  applied  to  this  system  have  shown  advantages 
not  possessed  by  other  systems;  but  it  remains  to  be  seen  whether 
this  idea  is  capable  of  the  extended  development  it  promises. 

Lodge=Muirhead  System.  Reference  has  already  been  made  to 
the  great  service  rendered  to  the  art  of  radiotelegraphy  by  Sir 
Oliver  Lodge  at  that  early  time 
when  its  future  depended  on  the 
elucidation  of  obscure  theoretical 
points  and  on  those  important 
practical  innovations  which  could 
alone  make  possible  a  commer- 
cial development  of  the  idea. 
Lodge  was  very  early  impressed 
by  the  fact  that  periodic  currents 
are  amplified  under  conditions  of 
resonance,  and  was  of  the  opinion 
that  wireless  telegraphy  by  the 
early  induction  method  could  be 
facilitated  by  properly  syntoniz- 
ing the  primary  and  the  secondary 
circuits.  He  accordingly  experimented  in  this  direction  and  success- 
fully verified  his  belief.  He  soon  abandoned  the  notion  of  inductive 
telegraphy,  however,  and  joined  forces  with  Dr.  Alexander  Muirhead, 
endeavoring  to  effect  wireless  telegraphy  by  means  of  Hertzian  waves. 
Always  keenly  aware  of  the  advantages  of  syntony  between  the  send- 
ing and  the  receiving  apparatus,  it  is  not  surprising  to  find  that  his 


Fig.  62.     Lodge  Conical  Capacity  Areas 


77 


78 


WIRELESS  TELEGRAPHY 


earliest  patent  specifications  were  very  copious  on  this  point.  To 
facilitate  accurate  tuning,  large  conical  capacity  areas  supported  by 
a  suitably  insulated  frame  structure  were  employed,  as  shown  in  Fig. 
62.  This  form  of  open  oscillatory  circuit  later  evolved  into  the  hori- 
zontal wire  areas  now  commonly  associated  with  the  Lodge-Muirhead 
system,  which  is  further  characterized  by  being  "ungrounded,"  the 
lower  capacity  being  in  some  cases  placed  several  feet  above  the  earth. 
One  form  of  a  Lodge-Muirhead  sending  and  receiving  station  is 
diagrammatically  represented  in  Fig.  63,  which  makes  clear  the 
form  of  capacity  areas  more  recently  adopted.  The  transmitter  is 
a  form  of  direct-coupled  closed  oscillatory  circuit,  and  the  receiving 
circuit  of  the  closed  inductively  coupled  type.  The  auxiliary  ap- 


Fig.  63.     Lodge-Muirhead  Sending  and  Receiving  Circuits 

paratus  used  in  conjunction  with  the  Lodge-Mi  lirhead  steel-disk 
coherer  previously  described  is  not  shown  in  the  drawing.  Dr. 
Muirhead,  endeavoring  to  render  the  system  serviceable  in  connection 
with  the  ordinary  forms  of  telegraphic  signaling  apparatus,  has  ap- 
plied a  syphon  recorder  directly  connected  with  the  coherer.  A 
Morse  register  has  also  been  employed,  or  a  telephone,  as  occasion 
suggested.  Automatic  transmission  by  means  of  perforated  tape  is 
sometimes  used,  a  perforator  being  furnished  with  their  equipment. 
The  Lodge-Muirhead  system  has  never  reached  the  large  indus- 
trial development  achieved  by  some  other  systems,  notably  the  Marconi 
and  the  Telefunken;  but  it  is,  nevertheless,  in  commercial  operation 
in  many  parts  of  the  world.  Communication  was  established  in 
1904  between  the  Andaman  Islands  and  the  mainland  of  Burma, 


78 


SYSTEMS  OF  RADIOTELE GRAPH Y  79 

and  has  given  excellent  service  since.  The  distance  is  slightly  over 
300  miles.  The  adverse  conditions  incident  to  a  tropical  climate 
were  here  admirably  met. 

Deforest  System.  One  of  the  best  known  American  systems  is 
that  developed  by  Dr.  Lee  DeForest  of  Chicago.  The  DeForest 
interests  have  many  stations  located  in  the  eastern  States  and  along 
the  Atlantic  seaboard,  one  of  the  largest  of  which,  located  at  Man- 
hattan Beach  near  New  York  City,  has  successfully  effected  com- 
munication with  Porto  Rico  and  Colon,  Panama,  the  latter  a  distance 
of  more  than  2,000  miles.  A  large  number  of  merchant  vessels  are 
equipped  with  this  make  of  apparatus.  The  United  States  navy  also 
possesses  a  number  of  sets. 

DeForest  was  among  the  first  to  employ  an  alternating-current 
transformer  to  charge  the  requisite  capacity.  The  earlier  form  of 
his  apparatus  included  a  small  motor-generator  set  delivering  current 
at  500  volts,  which  was  stepped  up  to  25,000  to  50,000  volts  by  means 
of  an  oil-immersed  transformer,  the  secondary  terminals  being  con- 
nected to  the  aerial  and  ground  with  condensers  across  a  gap  of  the 
disk  type.  The  receiver  circuit  used  in  conjunction  with  this  ap- 
paratus was  of  the  untuned  kind,  the  detector  being  of  an  electrolytic 
nature  called  a  "goo"  responder,  an  invention  of  DeForest  and 
E.  H.  Smythe.  A  "needle"  anti-coherer  of  extreme  simplicity  was 
used  with  the  earlier  equipments,  consisting  of  a  light  steel  needle 
upheld  by  a  retractile  spring  against  two  small  aluminum  rods.  A 
telephone  was  employed  to  respond  to  the  fluctuations  of  current  in 
a  local  battery  circuit  caused  by  the  increased  resistance  of  the  needle 
contacts  under  the  action  of  the  received  oscillations.  Great  sim- 
plicity was  aimed  at  in  the  design  of  the  entire  apparatus.  No 
attempt  was  made  to  accomplish  selection. 

Electrolytic  and  thermo-electric  detectors  have  been  the  subject 
of  extended  investigation  by  DeForest  and  his  co-workers.  As  a 
result  thereof  a  detector  was  evolved,  consisting  essentially  of  a  small 
containing  vessel  filled  with  a  suitable  electrolyte  into  which  projects 
the  tip  end  of  an  exceedingly  fine  platinum  wire.  This  "cell,"  under 
the  influence  of  oscillations,  exhibits  a  marked  difference  in  its  re- 
sistance to  a  local  current.  The  similarity  to  the  Fessenden  liquid 
barreter  is  apparent.  Much  controversy  has  arisen  relative  to  the 
theoretical  operation  of  these  detectors,  DeForest  contending  that 


79 


80 


WIRELESS  TELEGRAPHY 


the  action  was  electrolytic,  while  Fessenden  and  others  have  held  to 
the  view  that  the  observed  eft'ect  was  due  to  the  thermal  action  of  the 
oscillations.  Whatever  the  correct  explanation  may  be,  the  fact 
remains  that  the  "electrolytic"  detector  became,  in  the  hands  of 
DeForest,  an  exceedingly  sensitive  device  and  has  contributed  largely 
to  the  success  of  his  system. 

DeForest  later  devised  a  syntonized  system  based  upon  the  prin- 
ciple involved  in  the  so-called  "Lecher  Wires,"  which  reflect  waves 
bearing  a  definite  ratio  to  the  length  of  such  wires.  This  arrange- 
ment, exhibiting  anti-nodes  of  potential  and  current,  possesses  de- 


Fig.  64.    Clark  Sending  and  Receiving  Circuits 

cided  advantages  when  applied  to  the  receiving  circuit,  as  it  permits 
a  potentially-operable  or  current-actuated  detector  to  be  placed  at 
a  point  of  maximum  effectiveness.  Possessing  also  a  very  definite 
time-period,  this  form  of  circuit  was  found  to  lend  itself  admirably 
to  timing  purposes. 

Clark  System.  The  Clark  Engineering  Company  manufac- 
tures a  form  of  radiotelegraphic  apparatus  designed  by  Thomas 
E.  Clark,  which  is  usually  supplied  as  a  portable  equipment,  con- 
tained in  oak  cases  provided  with  shoulder  straps  for  carrying. 
Many  such  sets  have  been  purchased  for  the  Signal  Corps  of  the 


80 


SYSTEMS  OF  RADIOTELEGRAPHY 


81 


United  States  army,  for  which  service  they  are  especially  intended. 
The  aerial  wire  is  preferably  raised  by  means  of  a  kite.  The  trans- 
mitter is  of  the  inductively  coupled  type,  consisting  of  an  induction 
coil,  two  one-half  gallon  Leyden  jars,  the  oscillation  transformer, 
and  the  necessary  auxiliary  apparatus,  such  as  secondary  batteries, 
an  interrupter,  etc.  This  portion  of  the  equipment  is  made  to  be 
contained  in  three  cases,  while  the  receiving  equipment  is  economic- 
ally arranged  within  a  fourth  oak  box  covered  with  canvas.  The 
receptor  employed  is  of  the  auto-coherer  variety,  operating  under 


Fig.  65.     Stone  Sending  and  Receiving  Circuits 

the  variations  of  resistance  of  the  imperfect  contact  between  two  con- 
ducting plugs  of  steel  with  a  small  quantity  of  carbon  granules  inter- 
posed between  them.  A  head  telephone  receiver  and  one  dry- 
battery  cell  are  shunted  around  the  auto-coherer.  The  complete 
sending  and  receiving  circuits  of  the  Clark  system  are  shown  in  Fig. 
64.  It  will  be  noticed  that  the  system  presents  nothing  of  novelty 
beyond  the  fact  of  its  admirable  adaptability  to  the  requirements  of 
a  portable  equipment.  It  can  be  readily  packed  on  the  back  of  a 
transport  mule,  or  carried  by  men  in  a  military  campaign. 


81 


82 


WIRELESS  TELEGRAPHY 


Stone  System.  Another  American  system,  which  is  curiously 
enough  little  referred  to,  is  the  Stone  system,  invented  by  J.  S.  Stone, 
who  has  been  granted  nearly  one  hundred  patents  in  this  country 
alone,  besides  their  equivalents  in  European  countries.  His  specifica- 
tions cover  the  widest  possible  range  of  subjects  pertaining  to  radio- 
telegraphy  and  proclaim  him  to  be  the  possessor  of  an  extraordinary 
understanding  of  the  more  recondite  problems  connected  with  the 
science.  Several  of  his  patents  cover  the  inductive  coupling  of  aerials, 
something  after  the  manner  of  the  Braun-Marconi  method.  It  is 


Fig.  66.     Massie  Sending  and  Receiving  Circuits 

difficult  to  believe  that  any  large  proportion  of  the  specifications  have 
ever  been  tried  out  in  practice;  in  which  case  they  may  represent  but 
"anticipatory"  patents.  One  of  the  Stone  arrangements  for  the 
sending  and  receiving  stations  is  shown  in  Fig.  65,  which  embodies 
features  of  interest  particularly  from  the  viewpoint  of  the  "wireless" 
operator.  Reference  is  made  to  the  multiple  function  of  the  send- 
ing key  which  allows  an  operator  to  be  "broken  in  upon' 'while  send- 
ing, by  reason  of  the  fact  that  the  receiving  circuit  is  broken  by  the 
depression  of  the  key  but  instantly  closed  upon  release.  The  aerial 
is  inductively  coupled  to  the  closed  oscillatory  circuit  containing  a 


SYSTEMS  OF  RADIOTELEGRAPHY  83 

multiple-spark  gap.  Various  forms  of  detectors  have  been  used 
by  Stone,  especially  electrolytic  and  thermal  devices.  In  one  of  his 
patent  applications  he  describes  a  thermopile  of  platinum  and  gold 
for  use  as  a  detector.  The  Stone  system  has  never  been  widely 
exploited  although  such  equipments  are  occasionally  used  in  this 
country  and  doubtless  may  be  found  elsewhere. 

Massie  System.  Walter  W.  Massie  of  Providence,  R.  I.,  has 
developed  a  system  of  radiotelegraphy  which  bears  his  name.  While 
the  system  has  never  been  exploited  on  a  large  scale,  numerous  sets 
of  apparatus  have  been  purchased  by  the  United  States  government, 
and  many  private  concerns  find  use  for  this  make  of  apparatus. 
Massie  is  well  known  among  the  amateur  wireless  experimenters 
as  the  inventor  of  an  exceedingly  simple  detector  of  the  imperfect 
contact  type,  which  has  rendered  many  a  home-made  outfit  at  least 
operative  where  a  more  complicated  receptor  would  have  been  pro- 
hibitive. The  device  goes  under  the  name  of  the  oscillaphone,  and 
consists  simply  of  a  common  sewing  needle  placed  carefully  across 
two  sharpened  carbon  edges.  A  small  horseshoe  magnet  is  some- 
times located  under  the  needle  in  order  to  exercise  a  slight  attraction 
and  maintain  good  connection.  In  the  Massie  equipments  supplied 
for  long-distance  use,  an  electrolytic  detector  is  employed.  The 
Massie  circuits  are  shown  in  Fig.  66.  The  aerial  is  direct-coupled. 

Poulsen  System.  A  remarkable  system  due  to  the  genius  of 
Valdemar  Poulsen  of  Copenhagen  has  of  late  years  attracted  great 
attention,  as  it  undoubtedly  marks  a  decided  advance  in  the  art. 
Poulsen  has  accomplished  by  means  of  a  modification  in  the  Duddell 
arc  a  method  of  creating  an  almost  continuous  train  of  undamped 
oscillations  resulting  in  an  equivalent  train  of  electric  waves.  The 
ability  to  generate  such  a  persistent  train  of  waves  offers  great 
advantages  in  the  syntonization  of  stations  and  in  the  problem  of 
selective  signaling.  As  before  mentioned,  the  Poulsen  system  is 
characterized  by  the  employment  of  hydrogen  under  pressure  as 
the  surrounding  medium  for  the  arc.  The  receiving  device  used 
is  the  invention  of  Pederson,  and  a  very  full  description  .of  it  may  be 
obtained  by  referring  to  the  Electrician  for  Nov.  16,  1906. 

Other  Systems  and  Inventors.  Numerous  other  systems  of 
radiotelegraphy  have  been  exploited  in  various  countries,  but  space 
will  not  permit  of  a  detailed  description  of  them  here.  The  patent 


83 


84  WIRELESS  TELEGRAPHY 

files  of  every  government  contain  numberless  specifications  pertain- 
ing to  the  art;  indeed,  it  is  doubtful  if  any  other  improvement  in 
electrical  communication  has  called  forth  in  so  short  a  time  a  more 
voluminous  patent  literature. 

The  Rochefort-Tissot  system  in  France  has  met  with  considerable 
success.  Perhaps  the  most  distinctive  feature  of  this  system  is  the 
form  of  induction  coil  employed,  called  a  "unipolar  transformer." 
The  equipments  are  manufactured  by  Ducretet,  the  French  instru- 
ment maker. 

In  Belgium  the  Guarini  system  has  been  installed  in  various 
localities  with  moderate  success.  The  inventor  has  great  faith  in 
the  possibility  of  relaying  radiotelegraphic  messages  to  accomplish 
long-distance  transmission.  He  has  devised  a  relay  for  such  purposes, 
which  seems  to  promise  good  results. 

The  Russian  government  has  experimented  with  several  sys- 
tems, but  the  Popof  system  is  now  almost  exclusively  used.  Con- 
siderable interest  attaches  to  this  system  on  account  of  its  historical 
importance.  As  early  as  1895,  Prof.  Popoff  communicated  to  the 
Physico-Chemical  Society  of  St.  Petersburg  the  details  of  a  device 
employed  by  him  for  graphically  registering  atmospheric  disturbances 
of  an  electrical  nature  by  means  of  a  Coherer  introduced  between  an 
elevated  "exploring  rod"  and  the  ground.  A  relay  and  tapper  were 
also  employed,  the  former  serving  to  operate  a  Richards  register. 
It  is  thought  by  many  that  sufficient  credit  is  not  given  Popoff  for 
these  innovations. 

Sir  H.  M.  Hozier  and  S.  G.  Brown  in  England  have  developed 
a  system  bearing  their  names,  which  differs  little  from  the  other 
systems,  with  the  exception  of  the  detector  and  method  of  directly 
connecting  the  same  to  a  syphon  recorder.  The  Hozier-Brown 
detector  has  been  described  elsewhere. 

A  system  of  selective  signaling  which  seems  to  promise  well, 
is  that  named  after  the  inventor,  Anders  Bull.  Resonance  is  not 
employed  as  a  selective  agency;  instead,  the  receiver  is  designed  to 
respond  only  to  a  group  of  wave-trains  which  are  separated  by  certain 
unequal  and  predetermined  intervals  of  time.  The  mechanism 
effecting  the  transmission  of  such  properly  timed  wave  groups  is 
called  the  dispenser,  and  the  companion  device  at  the  receiving  end, 
the  function  of  which  is  to  translate  the  wave  groups  into  printed 


84 


SYSTEMS  OF  RADIOTELEGRAPHY  85 

Morse  characters,  is  called  the  collector.  Tests  conducted  by  the 
United  States  navy  with  this  system  were  highly  satisfactory  as  re- 
gards secrecy  and  freedom  from  atmospheric  disturbances.  The 
complicated  nature  of  the  apparatus  will  possibly  prohibit  the  ex- 
tensive use  of  this  system,  although  it  possesses  advantages  not  even 
theoretically  possible  by  resonance  alone. 

Conclusion.  During  the  twenty  years  or  so  since  Hertz  made 
his  famous  discovery  of  electric  waves,  radiotelegraphy  has  made 
many  substantial  advances  toward  the  goal  of  perfection;  and  it 
stands  today  a  conspicuous  and  brilliant  example  among  the  many 
resources  which  Science  has  contributed  to  modern  civilization. 
Its  uses  are  many  and  important.  To  mention  its  life-saving  power 
alone  is  to  secure  for  it  a  high  claim  to  consideration.  Its  success 
in  this  regard  has  been  spectacular  in  more  than  one  instance;  and 
it  is  not  too  much  to  say  that  radiotelegraphy  has  saved  hundreds 
of  lives  since  the  "wireless"  installation  of  ships  has  become  prevalent. 
To  travel  on  the  ocean  with  a  "wireless"  equipment  on  board,  know- 
ing that  in  case  of  peril  the  assistance  of  vessels  within  a  radius  of 
hundreds  of  miles  can  be  instantly  summoned,  adds  not  a  little  to 
the  comfort  and  security  of  the  passenger.  Radiotelegraphy  may 
indeed  be  said  to  have  struck  a  vital  blow  to  the  terrors  of  the  sea. 
The  sea,  it  would  seem,  has  become  the  chosen  sphere  of  wireless 
telegraphy,  since  it  fills  a  want  never  supplied  before.  Formerly 
ocean-bound  vessels  were  isolated  from  the  world  for  days  at  a 
time;  but  now  they  can  communicate  with  land  or  with  other  ships 
at  almost  any  point  in  their  course,  some  of  the  large  ocean  liners 
keeping  in  such  close  touch  with  events  that  they  publish  daily  bul- 
letins giving  the  world's  latest  news. 

Another  startling  achievement  of  radiotelegraphy  has  been  its 
success  in  effecting  trans-Atlantic  communication.  Messages  are 
sent  between  Europe  and  America  across  a  void  of  air  and  water 
some  3,000  miles  in  extent.  And  they  are  not  mere  test  messages, 
but  regular  press  telegrams  such  as  might  be  sent  by  cable.  Here 
radiotelegraphy  has  become  the  direct  rival  of  the  old  method 
of  wire  transmission.  Whether  the  one  will  ever  supersede  the  other 
is  a  question  open  to  debate.  The  probabilities  seem  to  be  in  favor 
of  wireless,  especially  if  the  present  rate  of  progress  continues;  but, 
for  the  present  at  least,  there  is  room  for  both  methods. 


85 


86  WIRELESS  TELEGRAPHY 

Wireless  telegraphy  promises  to  be  of  great  service  in  times  of 
war;  in  fact,  all  the  leading  nations  have  equipped  their  armies  and 
navies  with  radiotelegraphic  apparatus.  Battleships  will  have  a  facil- 
ity of  communication  never  before  possible,  and  land  forces  will  be 
equally  subserved.  Heretofore,  one  of  the  first  moves  of  a  belligerent 
force  was  to  cut  the  enemy's  telegraph  wires;  but  to  cut  off  an  electric 
wave  will  not  be  such  an  easy  matter.  The  Japanese  constantly 
made  use  of  wireless  telegraphy  in  the  late  war  with  Russia.  The 
Japanese  have  their  own  method  of  effecting  radiotelegraphic  com- 
munication, the  details  of  which  are  kept  secret;  but  that  it  works 
successfully,  they  have  well  demonstrated. 

Concerning  the  utility  of  radiotelegraphy  for  communicating 
across  land  areas,  much  that  is  favorable  and  promising  can  be 
recorded;  but  there  is  still  something  to  be  desired  with  respect  to 
ease  and  certainty  of  operation.  The  progress  thus  far  made  has 
brought  to  light  many  problems  which  await  solution  and  recorded 
many  phenomena  relative  to  transmission  over  long  distances,  espe- 
cially over  land,  which  cannot  as  yet  be  accounted  for  or  controlled. 
The  screening  effect  of  intervening  mountains  and  cliffs  exercises 
a  marked  difference  in  the  energy  of  the  received  signals;  long  stretches 
of  exceptionally  dry  ground  seern  to  have  the  same  effect.  This 
probably  accounts  for  the  fact  that  the  greatest  distances  to  which 
signaling  has  been  carried  have  been  over  salt  water.  Signals  seem 
to  be  more  easily  effected  at  night  than  in  daylight;  so  marked  is 
this  effect  that  communication  carried  on  with  perfect  success  at 
night  has  often  been  permanently  interrupted  by  the  advent  of  day- 
light only  to  be  resumed  the  following  night.  J.  J.  Thomson  has 
put  forward  a  possible  explanation  of  this,  but  space  forbids  its  in- 
clusion here.  Again,  certain  conditions  of  the  atmosphere  seem  to 
render  but  comparatively  small  energy  necessary  in  the  accomplish- 
ment of  long  distances  at  times. 

Thus  radiotelegraphy,  like  all  forms  of  telegraphy,  as  well  as 
telephony,  has  its  limitations  and  unsolved  problems;  but,  judging 
by  past  achievements,  it  is  not  well  to  dogmatize  too  emphatically 
as  to  the  finality  of  these  limits. 


86 


THE  FIRST   S2T   OF  WIRELESS  TELEPHONE  INSTRUMENTS   FOR 

THE   UNITED  STATES   NAVY 

Installed  on  the  Flagship  "Connecticut."     The  "Audion"  Receiver  with  Tuning  Device  on 
the  Top  at  Right,  the  Transmitter  on  the  Left. 


WIRELESS  TELEPHONY 

Wireless  telephony  is  not  so  new — almost  unborn,  indeed — 
as  is  generally  supposed.  Like  its  companion  art,  wireless  teleg- 
raphy, it  began  its  existence  well  back  in  the  nineteenth  century. 
Its  inception  is  contemporaneous  with  that  of  wire  telephony,  for 
Alexander  Graham  Bell  was  the  originator  of  both.  It  is  a  singular 
coincidence  that  Bell,  the  inventor  of  the  telephone,  and  Morse, 
the  reputed  inventor  of  the  telegraph,  should  each  have  been  among 
the  first  to  accomplish  their  respective  modes  of  communication 
wirelessly.  The  history  of  wireless  telephony  follows  very  closely 
that  of  wireless  telegraphy.  The  extreme  sensitiveness  of  the  tele- 
phone receiver  to  small  variations  of  current  very  naturally  sug- 
gested its  employment  as  a  receiving  device  in  connection  with  the 
inductive  and  conductive  methods  of  wireless  telegraphy,  and 
attempts  were  made  at  an  early  date  to  accomplish  the  transmission 
of  articulate  speech  by  these  same  means.  The  results  obtained 
however,  were  very  meager;  the  inherent  difficulties  characterizing 
these  methods  proved  to  be  even  greater  with  the  application  of 
telephone  principles,  due  to  the  diminution  of  energy  made  necessary 
by  the  nature  of  the  process.  As  in  the  case  of  wireless  telegraphy, 
the  solution  of  the  problem  lay  in  the  application  of  the  method  of 
electric  radiation. 

Bell's  Radiophone.  One  of  the  earliest  attempts  at  radioteleph- 
ony  was  not  of  an  electrical  nature,  judging  by  the  usual  appear- 
ances, but  depended  on  the  thermal  effect  of  a  variable  beam  of  light 
directed  upon  bits  of  burnt  cork  enclosed  in  a  small  glass  tube  to 
which  was  connected  a  rubber  tube  to  be  inserted  in  the  ear  of  a 
listener.  This  device  is  shown  in  Fig.  1.  The  light  from  a  con- 
venient source  was  reflected  from  a  thin  silvered  diaphragm  and 
caused  to  fall  upon  the  burnt  cork.  When  this  diaphragm  was  set 
into  vibration  through  the  agency  of  the  voice,  the  light  reflected 
therefrom  was  subjected  to  a  corresponding  variation  of  intensity,  ' 
and,  being  directed  upon  the  blackened  cork,  produced  therein 
minute  changes  of  volume  due  to  the  variations  of  temperature; 


89 


2  WIRELESS  TELEPHONY 

and  such  changes  produced  air-waves  which  were  manifested  in 
the  form  of  sound  and  audible  within  the  tube.  This  simple  device, 
invented  by  Alexander  Graham  Bell,  was  called  by  him  a  radio- 
phone. He  later  greatly  improved  the  apparatus  by  substituting 
selenium  as  the  means  of  reception,  the  peculiar  electrical  property 
of  which  substance  was  then  first  attracting  attention. 


Fig.  1.    Bell's  Kadiophone 

Selenium  Cell.  In  1873,  Willoughby  Smith  discovered  that 
the  resistance  of  metallic  selenium  was  greatly  reduced  by  exposure 
to  light.  The  light  from  a  small  gas  Burner  was  found  to  exercise 
a  marked  influence  on  the  conductivity  of  short  rods  of  selenium 
used  as  resistances  in  a  series  of  cable  tests  then  in  progress.  The 
discovery  caused  widespread  interest  in  the  scientific  world.  Among 
the  many  men  attracted  by  this  peculiar  property  of  selenium  was 
Prof.  Bell,  who,  in  conjunction  with  Sumner  Tainter,  succeeded 
in  producing  the  first  useful  so-called  "selenium  cell."  This  de- 
vice consists  essentially  of  selenium  spread  over  the  surface  pre- 
sented by  the  edges  of  alternate  disks  of  metal  separated  by  thin 
sheets  of  mica  after  the  manner  of  a  condenser,  thereby  greatly 
enlarging  the  area  of  contact  between  the  selenium  and  the  elec- 
trodes formed  by  the  alternate  disks.  By  connecting  such  a  cell 
in  series  with  a  battery  and  telephone  receiver,  the  current  passing 
through  the  circuit  is  largely  dependent  upon  the  degree  of  con- 
ductivity possessed  by  the  selenium  cell,  which  in  turn  depends  upon 
the  amount  of  light  falling  thereon.  Any  variation  of  the  light 
directed  upon  the  cell  is,  therefore,  capable  of  causing  a  correspond- 
ing variation  of  the  current  flowing  through  the  receiver,  with  the 
result  that  such  variations  become  audible  therein. 


90 


WIRELESS  TELEPHONY  3 

Bell's  Ph otophone.  In  1878  Bell  put  forward  a  most  ingenious 
application  of  the  selenium  cell  for  the  purposes  of  radiotelephony, 
which  he  called  a  photophone.  The  arrangement  of  apparatus  is 
shown  in  Fig.  2.  The  selenium  cell  C  is  placed  in  the  focus  of  a 
parabolic  reflector  R  and  is  thus  interposed  in  the  path  of  the  rays 
reflected  by  the  mirrored  surface  of  a  diaphragm  D  from  any 
suitable  source  of  light  S.  The  resistance  of  the  selenium  cell 
was  approximately  1,200  ohms  in  darkness,  and  about  half  that 
when  fully  illuminated.  The  mode  of  speech-transmission  is  so 
similar  to  that  of  the  radiophone  that  further  description  is  not 
necessary. 

The  photophone,  as  proposed  by  Bell,  may  be  made  to  trans- 
mit speech  perfectly  over  short  distances,  but  it  is  obviously  limited 
by  reason  of  the  inefficient  means  employed  to  effect  the  variation 
of  the  intensity  of  a  source  of  light.  As  the  employment 


SOURCE 


B 
\1 
T£FfY         LJ, 

'I  -  *[ 


ffZCE/VZft 


BA  TT£FfY 

' 


Fig.  2.     Bell's  Photophone 


of  the  device  for  distances  relatively  long  necessitated  the  use  of 
powerful  sources  of  light  and  adequate  means  for  controlling  the 
same,  the  invention  remained  but  a  beautiful  laboratory  experiment 
until  the  discovery  of  the  speaking  arc  by  Simon  in  1897  opened  up 
the  possibility  of  future  development. 

"Light  Telephony."  Prof.  H.  T.  Simon  of  the  Physical  Institute 
of  the  University  of  Erlangen  discovered,  toward  the  end  of  the  year 
1897.  that  a  direct-current  arc  may  be  made  to  give  forth  musical 
tones  and  even  speech  by  superimposing  a  telephonic  voice  current; 
upon  the  arc  current.  This  discovery  suggested  the  possibility  of 
using'  Simon's  arc  as  a  transmitting  arrangement  £01  the  BeJtl  photo- 


91 


4  WIRELESS  TELEPHONY 

phone.  With  this  end  in  view,  numerous  experiments  were  carried 
on,  principally  in  Germany,  aiming  to  increase  the  efficiency  of  the 
apparatus  when  operated  in  conjunction  with  powerful  search- 
lights, and  also  to  develop  the  selenium  cell  to  a  point  of  greater 
sensitiveness.  Wireless  telephonic  communication  by  this  means 
has  become  known  as  light  telephony,  and  has  reached  its  highest 
development  in  the  hands  of  that  most  ingenious  German  investigator, 
Ernst  Ruhmer.  The  German  navy  has  several  vessels  equipped 
with  the  Ruhmer  apparatus  for  intercommunication.  It  is  said  that 
a  distance  of  twenty  miles  is,  under  favorable  weather  conditions,  the 
limit  of  operativeness  with  this  form  of  radiotelephony.  The  use 
of  the  system  is  necessarily  restricted  to  open  spaces,  and  dependent 
upon  clear  atmosphere. 

Telephony  by  Means  of  Hertzian  Waves.  The  success  achieved 
by  Marconi  in  telegraphing  without  wires  inspired  many  investigators 
to  apply  the  Hertzian-wave  method  to  the  problem  of  telephony. 
As  early  as  1897  various  workers  became  imbued  with  the  idea  and, 
as  a  result,  a  number  of  systems  of  radiotelephony  have  grown  up 
contemporaneously  with  those  of  radiotelegraphy.  It  cannot  be 
said,  however,  that  the  results  accomplished  by  the  early  experi- 
menters in  this  field  gave  more  than  a  promise  of  future  usefulness 
for  this  method  of  communication,  the  distances  covered  being  ex- 
tremely small  in  proportion  to  the  complexity  of  the  apparatus  in- 
volved. In  many  instances,  however,  the  inventors  of  such  systems 
Jiad  a  clear  perception  of  the  fundamental  requirements,  and  felt 
confident  that  the  development  of  the  art  on  its  practical  side 
would  ultimately  make  possible  a  successful  application  of  their 
theories. 

The  principal  difficulty  encountered  in  the  application  of  Hertzian 
waves  to  the  problems  of  telephony  was  found  at  the  start  to  reside 
in  the  transmitting  portion  of  the  apparatus.  The  receiving  end 
offered  no  great  obstacle,  since  it  was  known  at  an  early  date  that 
many  of  the  detectors  used  in  connection  with  radiotelegraphy  would 
prove  suitable  for  the  reception  of  speech — providing  that  a  means 
could  be  discovered  to  effect  the  emission  of  wave-trains  whose 
energy  should  vary  in  accordance  with  the  vibrations  of  the  human 
voice.  The  fundamental  problem  of  radiotelephony  is  practically 
the  same  as  that  met  with  in  ordinary  wire  telephony — to  cause  a 


92 


WIRELESS  TELEPHONY  5 

distant  diaphragm  to  repeat  sympathetically  the  vibrations  of  a  dia- 
phragm against  which  the  energy  of  the  sounds  to  be  transmitted  is 
directed.  In  both  cases  the  efficiency  of  the  various  transformations 
of  energy  involved  in  the  process  is  of  prime  importance.  The 
current-carrying  capacity  of  the  carbon  transmitter  places  a  limit  on 
the  amount  of  energy  possible  to  utilize  telephonically.  This  restric- 
tion is  felt  to  a  marked  degree  when  the  device  is  associated  with 
the  necessarily  large  amount  of  energy  required  for  Hertzian-wave 
radiation  over  any  considerable  distance.  In  view  of  the  foregoing, 
it  is  not  surprising  to  find  that  early  experiments  in  radiotelephony 
were  directed  almost  exclusively  toward  a  solution  of  the  problem  of 
an  efficient  transmitting  apparatus. 

Many  attempts  were  made  to  accomplish  this  end  by  placing 
the  ordinary  microphone  transmitter  in  the  primary  of  an  induc- 
tion coil,  thus  serving  the  purpose  of  an  interrupter,  as  exemplified 
in  Dolbear's  early  wireless  telegraph  system.  Such  experiments 
only  sufficed  to  show  that  nothing  was  to  be  gained  in  this  way, 
largely  by  reason  of  the  before-mentioned  inherent  limitations  of 
the  telephone  transmitter.  The  problem  was  then  attacked  in 
another  manner,  viz,  by  endeavoring  to  modify  telephonically  a  train 
of  waves  of  a  constant  intermittency  radiating  from  a  continuously 
operating  source  of  oscillations,  such,  for  instance,  as  a  simple  radio- 
telegraphic  transmitter  without  a  primary  signaling  key.  Though 
this  method  allowed  a  much  greater  amount  of  energy  to  be  utilized, 
it  soon  became  evident  that  a  grave  difficulty  was  presented  due 
to  the  nature  of  the  radiations  from  such  an  arrangement.  The 
train  of  waves  thus  generated  is  not  continuous,  but  consists  of 
intermittent  wave-trains  separated  by  short  periods  of  time  during 
which  no  radiation  takes  place.  These  breaks  in  the  continuity 
of  the  train  are  often  of  greater  duration  than  the  individual  oscilla- 
tions due  to  one  complete  discharge  of  the  condenser;  they  conse- 
quently produce  in  the  telephone  receiver  a  continuous  buzz  which 
seriously  interferes  with  the  audibility  of  the  received  voice  vibrations. 
As  the  timbre  of  the  human  voice  depends  upon  overtones  and  upper 
harmonies  of  a  frequency  of  from  5,000  to  8,000  or  more,  the  pauses 
between '  oscillation  trains  also  interfere  with  clear  articulation 
whenever  their  frequency  drops  much  below  10,000  per  second. 
At  frequencies  of  from  20,000  to  50,000,  however,  this  feature  ceases 


93 


6 


WIRELESS  TELEPHONY 


to  be  a  hindrance.  The  success  of  the  method  of  telephonically 
varying  the  energy  emitted  from  a  continuously  operating  source  of 
radiation  was  seen,  therefore,  to  depend  upon  the  possibility  of  pro- 
ducing more  perfectly  sustained  oscillations  of  high  frequency. 
The  means  for  creating  oscillations  that  are  undamped  and  prac- 
tically continuous,  may  be  considered  the  greatest  problem  of  radio- 
telephony  relative  to  transmission.  At  the  present  time  there  are 
two  methods  of  accomplishing  such  persistent  radiations,  viz,  by 
employing  the  high-frequency  alternator,  or  by  using  some  form  of 
the  oscillating  arc.  The  last-named  method  has  been  developed, 
under  the  ministrations  of  Valdemar  Poulsen,  to  a  degree  of  efficiency 
that  promises  to  place  radiotelephony  on  a  commercial  basis.  The 
alternator  method  has  been  persistently  favored  by  Prof.  il.  A.  Fes- 
senden,  who  has  accomplished  some  remarkable  results.  Both 
methods  have  their  staunch  advocates,  each  possessing  its  own  peculiar 
advantages  as  well  as  limitations. 

Nature  of  a  High=Frequency  Telephone  Current.    The  foregoing 
paragraphs  have  indicated  briefly  the  general  theory  upon  which  the 


posmvr 


Fig.  3.     Diagram  Representing  High-Frequency  Current 

most  successful  systems  of  radiotelephony  have  been  developed.  It 
remains  to  consider  in  more  detail  the  nature  of  the  action  involved 
when  a  uniform  flow  of  undamped  oscillations  is  modified  by  the  va- 
riations of  a  voice  current. 

It  is  convenient  for  a  ready  understanding  of  the  matter  to  first 
consider  the  case  of  a  high-frequency  alternator  supplying  a  con- 
stant alternating  current  of  a  periodicity  somewhat  above  human 
audibility — say  50,000  cycles  per  second.  Supposing  such  a  current 
to  be  flowing  through  a  variable  resistance  such  as  a  telephone  trans- 
mitter, the  effect  of  an  increase  of  the  resistance  thereof  manifests 
itself  by  a  lessening  of  the  amplitude  of  each  individual  half-wave 
of  current;  while,  conversely,  a  decrease  of  the  resistance  manifests 
itself  by  an  amplification  of  the  current  half-waves.  When,  there- 


94 


WIRELESS  TELEPHONY  7 

fore,  the  resistance  is  made  to  vary  with  great  rapidity,  as  when  the 
diaphragm  of  the  transmitter  is  thrown  into  vibration  by  sound, 
the  effect  upon  the  alternating  current  flowing  therein  is  to  produce 
a  corresponding  change  in  the  maxii  um  value  of  each  half-wave. 


Fig.  4.     Diagram  Kepresenting  Variations  of  Amplitude 

As  the  energy  of  each  half-wave  may  be  represented  by  its  ampli- 
tude, it  is  evident  that  an  alternating  current  varying  in  this  manner 
exhibits  a  wave-form  of  energy  equivalent  in  many  respects  to  a  direct 
current  similarly  modified.  Figs.  3  and  4  illustrate  this  idea,  Fig.  3 
representing  the  steady  alternating  current  permitted  by  the  normal 
resistance  of  a  transmitter;  and  Fig.  4  showing  the  alterations  of 
amplitude  thereof  occasioned  by  the  variations  of  resistance  in  the 
said  transmitter.  It  will  be  noticed  that  the  maximum  instan- 
taneous values  may  be  greater  than  normal,  as  well  as  less,  due  to 
the  fact  that  the  resistance  of  a  transmitter  when  spoken  into  varies 
between  limits  above  and  below  its  resistance  when  at  rest.  Some 
idea  of  the  complexity  of  the  action  taking  place  under  the  conditions 
of  actual  practice  may  be  had  by  referring  to  the  wave-form  shown 
in  Fig.  5,  which  represents  the  current  curve,  or  oscillagram,  of  a 


Fig.  5.     Oscillagram  of  a  Telephone  Current 

telephone  current  produced  by  the  vowel,  long  6,  spoken  into  the 
transmitter.  In  forming  a  mental  conception  of  the  wave-form 
resulting  from  the  superimposing  of  a  telephonic  voice  current  upon 
a  high-frequency  oscillating  current,  the  enormous  difference  in 
their  respective  periodicities  must  be  borne  in  mind. 


95 


8  WIRELESS  TELEPHONY 

In  the  case  of  an  oscillation  generating  arrangement  which  does 
not  produce  a  perfectly  sustained  train  of  electric  waves  but  a  series 
of  partially  damped  wave-trains  separated  by  slight  breaks  of  con- 
tinuity, the  essential  conditio  i  for  success  in  connection  with  radio- 
telephonic  work  is  that  the  ii  terruptions  shall  not  take  place  at  an 
audible  frequency.  It  is  highly  probable  that  the  direct-current 
arc  method  of  creating  oscillations  does  not  produce  an  absolutely 
continuous  train  of  waves,  as  is  the  case  with  a  high-frequency  alter- 
nator, but,  on  the  contrary,  is  made  up  of  a  great  number  of  groups 
of  almost  undamped  oscillations  separated  by  an  interval  of  time, 
very  small  even  in  comparison  with  the  duration  of  each  group. 

Oscillation  Generators.  An  account  has  already  been  given, 
in  the  pages  devoted  to  Radiotelegraphy,  of  the  attempts  which 
have  been  made  to  construct  high-frequency  alternators  for  use  in 
the  production  of  continuous,  undamped  oscillations,  and  some 
description  given  of  such  machines.  Reference  has  also  been  made 
to  the  development  of  the  direct-current  arc  method  of  producing 
a  similar  result.  In  the  present  instance  it  is  not  deemed  necessary 
to  dwell  on  these  subjects  further  than  to  give  some  notion  of  the 
particular  devices  constructed  for  use  ^n  connection  with  the  mcst 
successful  systems  of  radiotelephony,  and  to  mention  those  modi- 
fications of  the  arc  method  which  have  been  found  to  give  the  best 
results  in  this  field  of  use. 

Undoubtedly  the  most  successful  high-frequency  alternators 
have  been  those  constructed  by  Prof.  Fessenden  for  use  in  his  ex- 
tensive experiments  in  radiotelephony  carried  on  at  the  Brant  Rock 
(Mass.)  Station  of  the  National  Electric  Signaling  Company.  This 
inventor  has  devised  several  such  machines,  one  of  them  having  an 
output  of  2  kilowatts  operating  at  80,000  cycles,  and  a  voltage  of 
225  volts.  This  machine  was  of  the  double  armature  type  with 
300  teeth  on  each,  direct-coupled  to  a  DeLeval  turbine.  A  similar 
generator  designed  for  use  on  shipboard  and  run  by  a  turbine  is 
capable  of  developing  3  kilowatts  at  a  frequency  of  about  100,000 
cycles.  Fessenden  has  also  designed  a  10-kilowatt  machine  of  a 
periodicity  of  100,000  per  second.  The  problem  of  properly  design- 
ing such  generating  units  and  constructing  them  on  a  commercial 
basis  cannot  as  yet  be  said  to  be  satisfactorily  solved;  it  is  generally 
felt,  however,  that  the  solution  of  the  problem  will  be  effected  at  no 


96 


WIRELESS  TELEPHONY  9 

distant  date,  at  which  time  this  method  of  producing  the  requisite 
oscillations  for  electric-wave  communication  will  supersede  in  many 
instances  the  more  complicated  and  less  constant  methods  now  in  use. 

There  are  in  use  at  the  present  time  various  arrangements  of 
the  direct-current  arc  employed  as  a  means  of  creating  alternating 
currents  of  great  frequency,  all  of  which  depend  for  their  operation 
upon  the  principle  of  the  Duddell  arc  but  differing  in  the  details 
of  application.  One  of  the  earliest  and  most  successful  of  these  is 
due  to  Poulsen,  who  achieves  extremely  high-frequency  oscillations 
of  great  energy  by  causing  the  arc  to  take  place  between  copper  and 
carbon  electrodes  enclosed  in  a  chamber  containing  hydrocarbon 
gas.  In  order  to  increase  the  energy  of  radiation,  Poulsen  later 
employed  several  arcs  in  series.  This  is  known  as  the  multiple-arc 
system,  and  has  been  developed  to  a  high  degree  by  die  Gesellschaft 
fur  Drahtlose  Telegraphic  of  Berlin. 

Telephonic  Control  of  Oscillations.  Radiotelephony  figuratively 
substitutes  in  place  of  the  metallic  line  of  ordinary  telephone  prac- 
tice a  continuous  stream  of  electric  waves  of  approximately  uniform 
strength.  By  varying  from  instant  to  instant  the  energy  of  this 
stream  of  waves  in  accordance  with  the  variations  of  air-pressure 
acting  against  a  transmitting  diaphragm,  a  transference  of  such 
energy-variations  is  effected  between  two  stations.  By  the  employ- 
ment of  suitable  translating  devices,  the  energy-vibrations  of  the 
wave-stream  may  be  made  to  undergo  a  transformation  resulting 
in  the  movement  of  a  second  diaphragm  which  exactly  duplicates 
the  vibrations  of  the  first,  and  the  variations  of  air-pressure  occasioned 
thereby  complete  the  cycle  of  energy-transformations  from  sound 
to  sound. 

It  is  to  be  noted  in  connection  with  the  foregoing  analysis  that 
it  is  not  the  entire  amount  of  energy  of  the  flow  of  waves  between 
stations  that  is  available  for  transformation  into  sound  at  the  receiv- 
ing end,  but  only  the  energy  represented  by  the  variations  of  this 
flow  of  waves.  Thus  the  problem  of  telephonically  controlling  a 
large  amount  of  energy  for  efficient  radiotelephonic  transmission 
is  to  effect,  by  means  of  the  energy  of  the  voice  vibrations,  a  maximum 
percentage  of  variation  in  the  energy  radiated.  With  the  methods 
employed  at  the  present  time  there  are  reasons  for  believing  that  this 
percentage  does  not  greatly  exceed  5  to  8  per  cent  of  the  total  energy. 


97 


10  WIRELESS  TELEPHONY 

In  this  respect  radiotelephony  differs  very  widely  from  radioteleg- 
raphy,  for  with  the  latter  the  entire  energy  of  radiation  is  available 
to  the  limit  of  our  ability  to  detect  it.  Some  of  the  inventors  claim 
a  greater  percentage  of  efficiency  for  their  respective  systems  of  radio- 
telephony.  Fessenden  has  devised  an  improved  form  of  transmitter 
which  he  states  produces  much  better  results. 

There  are  several  ways  .of  modifying  the  electric  oscillations 
set  up  in  a  transmitting  arrangement  for  the  purposes  of  radio- 
telephony.    The  method   generally  employed   involves   the  use   of 
some    form    of    carbon   transmitter  whereby  the 
variations  of  its  resistance  under  the  influence  of 
the  energy  of  the  voice  are  made  to  vary  the  os- 
cillatory current  directly,  or  a  local-battery  circuit 
similarly  affected  is  inductively  associated  with 
the  oscillatory  circuit.     Variations  in  the  emitted 
wave-train  may  also  be  accomplished  by  the  use 
of  a  condenser  transmitter  formed  by  a  thin  me- 
tallic diaphragm  separated  from  a  metallic  plate 
by  a  thin  layer  of  air  acting  as  dielectric,  the 
vibrations  of  said  diaphragm  producing  variations 
of  capacity  between  the  two  surfaces.     This  vari- 
able capacity  is  used  to  throw  the  aerial  in  and 
out  of  tune.     The  inductance  of  an  oscillatory 
FFessendenIcircu?tf      circuit   may  also  be  made  to  vary  by  means  of 
the  voice  and  produce  a  like  result.     One  of  the 
earliest  suggestions  relating  to  the  telephonic  control  of  the  energy 
of  oscillations  was  made  by  an  Italian,  Lonardi,  who,  in  1897,  pro- 
posed that  the  spark  balls  of  a  Righi  oscillator  connected  to  a  source 
of  constant  potential  be  made  to  vibrate  by  the  voice,  thereby  alter- 
ing the  length  of  the  spark  gap   and   causing  the   oscillator  to  be 
charged  to  greater  or  lesser  potentials,  and  thus  varying  the  energy  of 
the  emitted  waves. 

Transmitting  Circuits.  One  of  the  simplest  and  earliest  cir- 
cuits patented  for  use  in  connection  with  radiotelephony  is 
shown  in  Fig.  6.  It  is  due  to  Fessenden,  and  consists  of  a  high- 
frequency  alternator  connected  in  series  with  an  aerial,  a  telephone 
transmitter,  and  the  ground.  The  time-period  of  the  radiating  cir- 
cuit thus  formed  is  adjusted  to  the  periodicity  of  the  dynamo. 


98 


WIRELESS  TELEPHONY 


11 


AERIAL 


TK/WSM/TTER. 


The  patent  application  on  this  arrangement  was  filed  in  1901  at  a 
time  when  it  is  generally  believed  that  the  creation  of  electric  waves 
necessitated  an  abrupt  release  of  energy,  as 
exhibited  by  the  discharge  of  a  condenser. 
In  experiments  carried  on  with  this  arrange- 
ment in  1906,  a  distance  of  about  ten  miles 
was  covered,  the  generator  running  at  10,000 
revolutions  per  minute  and  developing  50 
watts  at  80,000  cycles  per  second.  The 
resistance  of  the  armature  was  about  6 
ohms.  An  electrolytic  cell  was  used  for  a 
detector. 

Another  method  of  effecting  the  tele- 
phonic variation  of  an  oscillatory  system  is 
shown  in  Fig.  7.  The  aerial  is  connected  to 
the  secondary  of  a  small  transformer,  the 
primary  winding  of  the  same  being  in- 
cluded in  a  local-battery  transmitter  cir- 
cuit. 

An  arrangement  for  use  with  the  arc  form  of  oscillation  generator 
is  shown  in  Fig.  8.  Direct  current  for  the  arc  is  supplied  to  the 
terminals  of  the  closed  oscillating  circuit  through  the  secondary  of 


Fig.  7.     Transmitter  Induc- 
tively Associated  with  Aerial 


Fig   8.     Transmitter  Associated  with  the  Supply  Circuit 

a  transformer,  the  primary  circuit  of  which  contains  a  carbon  trans- 
mitter and  local  battery.  The  fluctuations  of  intensity  of  the  oscil- 
lations may  be, effected  in  a  manner  diagrammatically  shown  in 


99 


12 


WIRELESS  TELEPHONY 


Fig.  9,  where  the  inductive  method  of  superimposing  the  telephone 
current  from  a  local  circuit  is  applied  directly  to  the  closed  oscilla- 
tory circuit.  Inductances  I  and  I'  inserted  in  the  supply  mains 


EARTH 


Fig.  9.     Transmitter  Inductively  Associated  with  the  Closed 
Oscillatory  Circuit 

prevent  the  voice  current  from  passing  around  through  the  source 
of  supply. 

In  Fig.  10  is  shown  still  another  method  of  locating  the  variable- 
resistance  member,  viz,  by  shunting  the"  secondary  of  the  oscillation 


AERIAL 


EAffTH 


Fig.  10.     Transmitter  Shunted  across  the  Aerial  Inductance 

transformer  employed  in  connection  with  an  inductively  coupled 
aerial.  The  telephone  transmitter  may  also  be  used  with  a  directly 
coupled  aerial  by  causing  it  to  vary  the  effective  turns  of  a  portion 
of  the  inductance  included  in  the  open  radiating  circuit,  as  in  Fig.  11. 


100 


WIRELESS  TELEPHONY 


13 


From  the  circuits  here  given,  it  is  evident  that  the  conditions 
essential  to  telephony  are  fulfilled  when  the  transmitter  is  so  placed 
as  to  produce  by  its  action  a  change  of  the  electrical  properties  of 
the  radiating  aerial;  and  experience  has  shown  that  this  may  be 
accomplished  with  the  microphonic,  or  carbon,  transmitter  in  a 
variety  of  ways,  many  of  which  seem  to  operate  with  equally  good 
effect.  The  condenser,  or  variable-capacity,  transmitter  is  effectively 
operative  only  in  conjunction  with  the  oscillatory  portions  of  the 
sending  circuit,  usually  as  a  shunt.  One  method  of  placing  this  form 


ARC 


EARTH 


Fig.  11.     Transmitter  Shunted  across  a  Portion  of  the 
Aerial  Inductance 

of  transmitter  is  shown  in  Fig.  12,  which  arrangement  has  been  em- 
ployed by  Fessenden.  ," 

As  before  remarked,  the  small  current-carrying  capacity  of  the 
microphonic  transmitter  has  proved  to  be  a  great  obstacle  to  the 
rapid  development  of  the  art  of  radiotelephony  as  a  commercial 
proposition;  and  it  may  be  said  that  until  an  efficient  means  is  de- 
vised for  overcoming  this  difficulty,  and  thereby  greatly  increasing 
the  percentage  of  variation  in  the  intensity  of  the  oscillations,  or 
the  equivalent  thereof,  the  sphere  of  usefulness  for  this  form  of 
wireless  communication  will  be  much  restricted.  Many  attempts 
have  been  made  to  effect  this  improvement  by  connecting  several 
transmitters  in  multiple  to  be  acted  on  by  a  common  mouthpiece. 
Various  so-called  telephonic  repeaters  have  also  been  devised  pur- 
porting to  accomplish  an  increase  in  the  amplitude  of  the  telephonic 


101 


14 


WIRELESS  TELEPHONY 


AER/AL 


CONDENSER 
TRANSMITTER* 


current  Such  devices,  however,  have  not  proved  to  be  a  satisfac- 
tory solution  of  the  problem,  although  Fessenden  claims  to  be  able 
to  effect  a  decided  amplification  with  an  instrument  of  the  latter 
character  designed  by  himself.  This  ingenious  investigator  has 

undoubtedly  constructed  an  instrument 
more  nearly  fulfilling  the  requirements 
of  a  transmitter  adapted  to  this  class  of 
work  than  any  heretofore  presented.  It 
is  called  by  him  a  "trough"  transmitter, 
and  is  said  to  be  able  to  carry  continu- 
ously more  than  10  amperes.  The  elec- 
trodes are  water-jacketed  The  amount 
of  variation  in  a  current  of  this  magni- 
tude, produced  by  the  action  of  the  voice, 
is  of  course  the  important  factor.  The 
results  accomplished  by  the  "trough" 
transmitter  indicate  a  decided  gain  over 
the  form  commonly  employed.  Further 
radical  improvements  in  transmitter  de- 
sign may  be  confidently  expected  from 
the  numerous  experimenters  whose  irtventive  ability  is  now  being 
brought  to  bear  on  the  problem. 

Receiving  Arrangements.  For  purposes  of  radiotelephony  the 
detectors  depending  upon  mere  potential  for  their  operation,  such  as 
the  early  forms  of  coherer,  are  practically  useless.  The  essential 
characteristic  which  a  detector  suitable  for  this  class  of  work  must 
possess  is  that  it  shall  not  only  respond  to  the  received  oscillations, 
but  that  it  shall  be  affected  to  a  certain  extent  in  proportion  to  the 
amplitude  of  such  oscillations.  In  short,  radiotelephony  requires 
a  form  of  detector  which  is  quantitative,  that  is,  one  which  will 
respond  to  the  varying  integral  value  of  the  oscillating  current. 
Such  devices  as  the  thermo-electric,  electrolytic,  ionized  gas,  and 
crystal-valve  detectors  are  all  of  this  type,  and  may  be  used  for  the 
reception  of  speech  when  properly  connected  with  a  telephone  re- 
ceiver. This  quantitative  function  may  be  elucidated  by  consider- 
ing the  action  of  a  thermo-electric  detector  properly  associated  with 
a  tuned  receiving  circuit.  If  a  continuous  train  of  undamped  waves 
falls  upon  the  aerial,  their  effect  on  the  detector  is  to  increase  its 


Fig.  12.     Condenser  Transmitter 


102 


WIRELESS  TELEPHONY 


15 


resistance  by  raising  its  temperature,  and  thereby  decrease  the 
amount  of  current  flowing  through  the  telephone  receiver.  As  long 
as  the  flow  of  such  waves  remains  constant,  their  heating  effect  upon 
the  fine  platinum  wire  of  the  detector,  and  consequently  its  resist- 
ance, remains  constant,  and  no  sound  is  heard  in  the  receiver.  If, 
however,  the  wave-train  which  strikes  the  aerial  be  of  a  fluctuating 
nature,  due  to  the  vibrations  of  the  distant  telephone  transmitter, 
the  variations  of  amplitude  of  the  received  oscillations  will  cause  a 
corresponding  variation  in  their  heating  effect  on  the  platinum  wire, 
accompanied  by  like  variations  in  its  resistance,  whereupon  the 
current  flowing  through  the  telephone  receiver  will  be  similarly 
varied,  with  the  result  that  the  diaphragm  is  thrown  into  vibrations 
exactly  imitating  the  movement  of  the  transmitting  diaphragm. 

There  have  been  pre- 
viously described  under  the 
head  of  radiotelegraphic  de- 
tectors almost  all  the  devices 
used  for  a  similar  purpose 
in  connection  with  radio- 
telephony.  In  view  thereof 
it  is  not  thought  necessary 
to  devote  more  space  to  the 
subject  here,  further  than 
to  call  attention  to  a  form 
of  telephone  receiver  in- 
vented by  Fessenden  and 
called  by  him  a  "hetero- 
dyne" receiver,  a  most  ingenious  application  of  the  Bell  instrument 
to  the  purposes  of  space  telephony.  The  device  consists  of  two  small 
coils  of  wire,  one  of  which  is  wound  upon  a  stationary  laminated 
core  composed  of  very  fine  soft-iron  wires;  the  second  coil,  held  in 
close  proximity  to,  and  co-axial  with,  the  first,  is  attached  to  the  center 
of  a  thin  mica  diaphragm.  A  high-frequency  current  from  a  local 
source  is  maintained  through  the  stationary  coil.  The  other  coil,  ar- 
ranged to  vibrate  with  the  diaphragm,  is  connected  in  the  receiving 
oscillation  circuit,  as  shown  in  Fig.  13.  The  periodicity  of  the  local 
alternating  current  is  adjusted  to  approximately  the  same  frequency 
as  the  received  waves,  thereby  creating  a  mechanical  force  exerted  be- 


Fig.  13.     Heterodyne  Receiver  Circuit 


103 


16  WIRELESS  TELEPHONY 

tween  the  two  coils — a  force  which  varies  with  every  fluctuation  of  the 
intensity  of  the  received  oscillations,  and  results  in  vibrations  of  the 
mica  diaphragm  corresponding  to  those  of  the  distant  transmitter. 
When  this  device  is  used  as  a  detector  in  connection  with  radio- 
telegraphy,  the  frequency  of  the  local  source  of  current  is  purposely 
made  to  be  slightly  different  from  the  frequency  of  the  received  oscil- 
lations; under  which  condition  the  physical  phenomenon  known  as 
''beats"  is  engendered.  This  is  due  to  the  fact  that  at  certain  equal 
intervals  the  two  wave-form  currents  agree  in  phase  and  reinforce 
each  other,  while  at  times  midway  between  two  such  successive 
agreements  they  are  opposite  in  phase  and  tend  to  neutralize  each 
other.  These  intervals  of  maximum  reinforcement  occurring  at  an 
audible  frequency  produce  in  the  receiver  a  musical  note  of  a 
duration  depending  upon  the  length  of  the  Morse  dot  or  dash. 
By  means  of  this  simple  process,  it  is,  therefore,  possible  to  pro- 
duce audible  tones  by  the  interaction  of  two  alternating  currents 
whose  respective  frequencies  are  far  above  audibility.  The  het- 
erodyne receiver  is  almost  entirely  unaffected  by  atmospheric 
disturbances,  and  seems  to  offer  exceptional  possibilities  in  con- 
nection with  multiplex  transmission,  as  well  as  selective  communica- 
tion. 

Two=Way  Transmission.  In  wire  telephony  simultaneous  talk- 
ing and  listening  is  possible  by  reason  of  the  simple  nature  of  the 
circuits  and  because  of  the  comparatively  small  amount  of  energy 
involved  in  telephonic  transmission.  Radiotelephony  presents  in 
this  regard  difficulties  which  tax  to  the  utmost  present  inventive 
ability.  Without  special  appliances  it  is  of  course  necessary  after 
talking  to  throw  over  a  listening  key  or  switch  in  order  to  receive  the 
reply.  The  introduction  of  this  manual  operation,  while  not  of  a 
nature  to  greatly  detract  from  the  usefulness  of  this  method  of  com- 
munication, interferes  to  an  appreciable  extent  with  that  ease  of 
operation  we  are  accustomed  to  associate  with  the  telephone,  and 
destroys  the  illusion  of  the  actual  presence  of  the  person  spoken  to. 
It  cannot  well  be  expected  in  an  art  so  young  that  minor  details  of 
this  nature  should  have  been  thoroughly  perfected.  Arrangements 
for  simultaneous  talking  and  listening  have  already  been  put  for- 
ward, and  some  have  met  with  more  or  less  practical  success.  Fes- 
senden  has  patented  several  such  devices — one  involves  the  use  of 


104 


WIRELESS  TELEPHONY  17 

a  commutator  which  connects  the  transmitter  and  receiver  to  the 
aerial  in  very  rapid  alternation;  another  and  a  more  practicable  method 
is  called  by  him  the  "balance"  method,  and  consists  in  the  applica- 
tion of  the  "bridge"  together  with  a  "differential"  arrangement  often 
employed  in  duplex  telegraphy,  the  complete  circuit  requiring  a 
"phantom,"  or  artificial,  aerial.  The  detector  is  unresponsive  to  the 
powerful  oscillations  emanating  from  the  same  station,  but  sensitive 
to  the  oscillations  from  the  distant  station.  This  "balance"  method 
materially  cuts  down  the  loudness  of  the  received  sounds. 

Radiotelephonic  "calling"  is  accomplished  by  radiotelegraphic 
methods.  A  coherer  associated  with  a  local  battery  and  relay  is 
sometimes  employed  to  ring  an  electric  call  bell.  In  such  cases  it 
is  necessary  to  provide  means  for  cutting  out  the  coherer  and  relay 
during  conversation.  Under  conditions  where  it  is  impractical  to 
achieve  the  operation  of  a  relay,  it  becomes  necessary  to  keep  an 
operator  on  duty  "listening  in." 

Systems  of  Radiotelephony.  Radiotelephony  undoubtedly  pos- 
sesses many  advantages  over  radiotelegraphy,  not  the  least  of  which 
is  the  fact  that  a  skilled  operator  is  not  required  to  translate  the 
dot-and-dash  signals.  The  transmission  of  intelligence  is  more 
direct  and  expeditious,  and  in  times  of  emergency  this  might  become 
an  advantage  of  great  importance.  No  form  of  communication  is 
so  satisfying  as  that  of  speech.  It  is  due  to  this  fact,  perhaps,  that 
ordinary  wire  telephony  stands  today  superior  to  the  older  art  of 
telegraphy  in  point  of  development.  The  future  may  record  a 
similarly  greater  development  of  radiotelephony  than  will  be  ac- 
corded to  its  companion  art;  but  at  the  present  time  it  cannot 
be  said  to  compare  with  radiotelegraphy  as  regards  efficiency  and 
simplicity  of  apparatus.  Its  weak  points  are  known  and  under- 
stood, however,  and  every  effort  is  being  made  to  remove  the  ob- 
stacles that  stand  in  the  way  of  a  more  efficient  utilization  of  the 
means  employed. 

While  still  susceptible  of  great  improvement,  and  in  many 
cases  requiring  a  multiplicity  of  complicated  apparatus,  there  are 
a  number  of  radiotelephonic  systems  which  have  been  exploited  in 
the  various  countries,  many  of  which  are  in  regular  service.  Nearly 
all  of  the  large  navies  of  the  world  are  supplied  with  equipment  for 
intercommunication  between  the  different  vessels  of  a  fleet.  Among 


105 


18 


WIRELESS  TELEPHONY 


the  most  successful  systems  may  be  mentioned  the  Telefunken  and 
Ruhmer  systems  in  Germany,  the  Poulsen  system  in  Denmark, 
the  Marjorana  system  in  Italy,  and  in  America  the  systems  developed 
by  Fessenden,  DeForest,  and  Collins.  Many  other  systems  are 
known,  but  they  exist  in  a  more  or  less  imperfect  state  of  develop- 
ment. 

Telefunken  System.  Die  Gesellschaft  fur  Drahtlose  Tele- 
graphic of  Berlin  has  put  forward  one  of  the  most  thoroughly  de- 
veloped systems  of  radiotelephony  in  commercial  operation  at  the 
present  time.  It  is  generally  known  as  the  Telefunken  system, 
which  is  the  name  applied  to  the  radiotelegraphic  system  operated 
by  the  same  company. 

The  Telefunken  radiotelephonic  system  is  of  the  oscillating-arc 
type.  The  arrangement  of  circuits  is  shown  in  Fig.  14.  Six  or 


CHOKE  CO/L^ 


Fig.  14.     Transmitter  Circuit  of  the  Telefunken  System 

twelve  electric  arcs,  connected  in  series  and  shunted  by  an  inductance 
and  capacity,  form  the  source  of  the  high-frequency  oscillations. 
The  energy  supplied  to  this  portion  of  the  circuit  is  derived  from 
a  direct-current  source  of  220  or  440  volts  (if  the  latter,  12  arcs  in 
series  are  used)  connected  through  a  rheostat,  an  ammeter,  and  a  choke 
coil.  The  choke  coil  is  used  to  prevent  the  oscillatory  current  from 
passing  through  the  dynamo.  A  hot-wire  ammeter  is  included  in  the 
oscillatory  circuit,  and  another  between  the  aerial  and  the  ground, 


106 


WIRELESS  TELEPHONY 


19 


used  for  tuning  purposes.  When  the  circuits  are  in  exact  resonance, 
these  instruments  give  a  maximum  reading,  thus  affording  a  very 
convenient  means  of  ascertaining  if  the  system  is  in  proper  adjust- 
ment at  any  time.  An  adjustable  condenser  is  provided  in  the  oscil- 
latory circuit,  and  a  variable  inductance  in  the  aerial,  to  facilitate 
tuning.  It  will  be  noted  that  the  carbon  transmitter  is  associated 
with  the  aerial  as  a  shunt  around  the  secondary 
of  the  oscillation  transformer.  An  ordinary 
transmitter  is  used  and,  in  practice,  means  are 
provided  for  opening  the  transmitter  circuit 
while  calling,  and  at  other  times  when  it  is  de- 
sired to  protect  the  transmitter  from  the  detri- 
mental effects  of  continued  exposure  to  the 
heavy  current. 

The  electrodes  employed  for  the  arcs  in 
this  system  possess  features  of  interest.  The 
positive  member  is  formed  by  a  copper  tube 
about  2J  inches  in  diameter  and  8  inches  long 
closed  at  the  bottom  by  a  concave  piece  of  the 
same  material.  The  internal  cavity  is  filled 
with  water,  thus  serving  to  keep  the  metal  cool. 
Fig.  15,  which  shows  the  Telefunken  electrodes, 
represents  the  positive  member  as  partially  cut 
away  in  order  to  make  clear  the  construction.  The  negative  elec- 
trode is  of  carbon  \\  inches  in  diameter,  set  well  up  in  the  con- 
cave portion  of  the  positive  electrode,  but  separated  therefrom  by 
a  gap  of  about  \  inch.  The  arc  formed  between  these  two  mem- 
bers tends  to  maintain  the  uniformity  of  the  gap.  It  is  claimed 
that  the  consumption  of  carbon  is  only  about  1  inch  in  nearly  300 
hours,  and  that  the  copper  electrode  is  not  appreciably  affected 
by  the  arc.  The  water  is  changed  as  often  as  required,  according 
to  the  time  it  is  subjected  to  the  heat  of  the  arc,  or  by  reason  of 
evaporation.  Means  are  provided  for  the  adjustment  of  each  in- 
dividual arc,  and  for  the  simultaneous  striking  of  all.  The  fre- 
quency usually  achieved  by  this  method  is  approximately  375,000 
cycles  per  second.  The  equipments  are  rated  something  under  one 
kilowatt  for  connection  with  220  volts. 

The  receiving  arrangement  used  with  this  system  is  of  the 


Fig.  1 5.     Telefunken 
Electrodes 


107 


20 


WIRELESS  TELEPHONY 


simplest  kind,  consisting  of  a  detector  (electrolytic  or  thermo-electric) 
and  telephone  directly  coupled  to  the  aerial,  such  as  are  commonly 
employed  with  radiotelegraphy.  The  entire  apparatus  is  very  com- 
pact, requiring  but  little  space,  and  may  be  conveniently  placed  on 
a  small  table.  A  distance  of  25  to  45  miles  may  be  very  well  covered 
with  the  Telefunken  sets  such  as  are  supplied  for  use  on  shipboard, 
and  equipments  of  greater  power  may  be  had.  Simultaneous  talking 
and  receiving  is  not  provided  for  in  this  system. 

Ruhmer  System.  The  system  due  to  Ernst  Ruhmer,  the  Ger- 
man investigator,  well  known  for  his  extensive  work  in  connection 
with  the  development  of  "light  telephony"  and  for  his  researches 


Fig.  16.     Circuits  of  Ruhmer  System 

into  the  properties  of  selenium,  is  characterized  by  the  use  of  an 
oscillatory  arc  burning  in  hydrogen  or  other  suitable  gas.  The 
Ruhmer  circuits  are  shown  in  Fig.  16.  A  local-battery  transmitter 
circuit  is  employed  to  superimpose,  by  means  of  an  induction  coil, 
the  voice  current  upon  the  supply  terminals  of  the  oscillatory  portion 
of  the  arrangement.  A  direct-current  dynamo  of  440-volt  pressure 
is  used.  The  transmitting  aerial  is  inductively  coupled  to  the  closed 
oscillation  circuit.  Many  different  forms  of  arc  have  been  experi- 
mented with  by  this  inventor,  some  with  a  magnetic  blow-out.  Sim- 
plicity of  apparatus  has  been  aimed  at.  The  receiving  arrangement 
consists  of  an  electrolytic  detector,  battery,  and  telephone  receiver 


108 


WIRELESS  TELEPHONY 


21 


connected  with  the  aerial  and  its  associated  capacity  and  inductance. 
By  using  fairly  low  antennae,  the  Ruhmer  system  has  operated  very 
successfully  over  comparatively  short  distances. 

Poulsen  System.  Special  interest  attaches  to  the  Poulsen  system 
by  reason  of  the  fact  that  the  development  of  the  arc  method  of  pro- 
ducing sustained  high-frequency  oscillations  was  largely  due  to  the 
initiative  of  this  investigator.  Mention  was  made  of  the  Poulsen 
modification  of  the  singing  arc  in  its  application  to  radiotelegraphy. 
Fig.  17  represents  diagrammatically  its  application  to  a  system  of 
radiotelephony.  A  direct  current  from  a  suitable  source  is  applied 
to  the  terminals  of  the  arc  through  the  secondary  of  a  small  trans- 


Fig.  17.     Circuits  of  Poulsen  System 

former,  in  the  primary  of  which  is  placed  a  local  battery  and  tele- 
phone transmitter.  The  aerial  is  directly  coupled,  and  two  oil- 
condensers  are  so  located  as  to  prevent  the  direct  current  from 
reaching  the  aerial  or  ground.  The  magnetic  blow-out  devices 
are  not  shown  in  the  cut.  At  the  receiving  station  the  aerial  is  in- 
ductively coupled  with  a  closed  oscillatory  circuit  wrhich  is  connected 
with  a  local-battery  circuit  containing  the  detector  and  a  telephone 
receiver. 

Poulsen  has  constructed  many  forms  of  the  copper-carbon  arc 
burning  in  a  magnetic  field  in  an  atmosphere  of  gas.  In  order  to 
meet  the  difficulties  caused  by  the  irregularity  of  action  due  to  the 


109 


22  WIRELESS  TELEPHONY 

unequal  burning  of  the  carbon,  he  employs  in  connection  with  one 
form  of  his  arc  a  cylindrical  carbon  electrode  of  large  diameter 
which  is  slowly  rotated,  thus  presenting  constantly  a  new  surface  for 
the  arc.  In  another  modification,  the  same  result  is  accomplished 
by  means  of  a  rotary  magnetic  field  which  acts  directly  on  the  arc, 
causing  the  latter  to  constantly  change  its  position  on  the  surface  of 
the  electrodes.  He  has  also  employed  various  gases  through  which 
the  arc  is  maintained.  In  the  commercial  equipments  more 
recently  put  out,  the  gas  is  supplied  by  alcohol  allowed  to  drip 
slowly  into  the  arc  chamber,  at  a  rate  of  about  one  drop  every 
half  second. 

The  transmitter  employed  by  Poulsen  is  essentially  the  common 
carbon-granule  device;  he  has,  however,  effected  the  variation  of  his 
oscillations  by  means  of  a  multiple  transmitter  consisting  of  seven  or 
eight  such  instruments  connected  in  multiple  and  arranged  to  be 
acted  upon  by  one  mouthpiece. 

Successful  telephonic  communication  has  been  accomplished 
over  distances  varying  from  a  few  miles  up  to  three  hundred.  Poulsen 
long-distance  stations  are  located  at  Lyngby,  Denmark;  at  Berlin, 
Germany;  and  at  Cullercoats  near  Newcastle,  England;  and  smaller 
stations  are% located  in  Denmark  and  elsewhere.  The  aerial  used  at 
Lyngby  for  long-distance  transmission  is  about  225  feet  high,  and 
is  of  the  umbrella  type  composed  of  24  strands  of  phosphor-bronze 
wire.  A  20-horse-power  gasoline  engine  operates  a  10-kilowatt, 
500-volt,  direct-current  dynamo  for  the  arc.  A  phonograph  record 
has  been  transmitted  from  this  station  to  Berlin  and  distinctly  heard 
there — a  distance  of  325  miles. 

The  Marjorana  System.  In  Italy  radiotelephonic  experiments 
have  been  carried  on  by  Prof.  Quirino  Marjorana,  resulting  in  the 
successful  transmission  of  the  voice  from  Rome  to  Messina,  a  dis- 
tance of  about  312  miles.  As  a  means  of  creating  the  required  oscilla- 
tions, the  Marjorana  system  employs  an  arc  essentially  identical  with 
that  used  by  Poulsen.  The  transmitting  arrangement,  however,  is 
characterized  by  a  peculiar  manner  of  accomplishing  the  variations 
of  intensity  of  the  radiated  waves.  The  complete  circuit,  including 
diagrammatic  representation  of  the  Marjorana  liquid  microphone, 
or  transmitter,  is  shown  in  Fig.  18.  The  aerial  is  inductively  coupled 
with  the  source  of  oscillations.  The  arc  is  fed  through  the  blow-out 


no 


WIRELESS  TELEPHONY 


23 


magnets,  which  thus  serve  as  choke  coils  to  prevent  the  high-fre- 
quency current  from  flowing  through  the  direct-current  dynamo, 
which  acts  as  supply.  The  receiving  portion  of  the  system  possesses 
no  points  of  novelty,  as  it  is  of  the  simple  inductively  coupled  type 
and  employs  any  of  the  well-known  detectors  suitable  for  this  class 
of  work. 

It  is  the  transmitter  which,  as  suggested  above,  forms  the  dis- 
tinguishing feature  of  this  system.  Its  action  is  based  upon  the  fact 
observed  by  Marjorana  that  a  steady  stream  of  water  falling  from 
an  elevated  containing  vessel  through  a  small  orifice  may  have  its 
uniformity  modified  by  extremely  minute  mechanical  jars  imparted 


\ABf64L 


AEWAL 


Fig.  18.     Circuits  of  Marjorana  System 

to  the  containing  vessel.  The  liquid  transmitter  is  designed  to  take 
advantage  of  this  property,  and  is  shown  partially  in  section  in  the 
illustration.  A  stationary  rigid  containing  vessel  V  terminates  at  its 
lower  end  in  a  small  hole  through  which  the  water,  constantly  sup- 
plied to  said  vessel,  is  allowed  to  flow  continually  in  the  form  of  a 
minute  stream.  Interposed  in  the  path  of  this  stream  is  a  small  gap 
in  the  aerial  formed  by  two  platinum  points  separated  a  short  dis- 
tance. The  stream  completes  the  connection  across  this  gap.  Means, 
in  the  form  of  a  thin  diaphragm  introduced  as  a  portion  of  the 
wall  of  the  containing  vessel,  are  provided  to  affect  the  diameter 
and  contour  of  the  stream  in  accordance  with  the  vibrations  of  the 
voice.  The  center  of  this  diaphragm  is  connected  by  a  light  rod 
to  the  center  of  another  diaphragm  which  is  acted  upon  by  the 


ill 


f 


24  WIRELESS  TELEPHONY 

voice  through  suitable  mouthpiece.  The  action  is  as  follows:  The 
vibrations  of  the  double  diaphragm  are  communicated  to  the  volume 
of  the  liquid  in  the  form  of  variations  of  pressure  manifested  at  the 
orifice  and  resulting  in  similar  variations  in  the  volume  of  water 
constituting  the  stream.  Such  modifications  of  the  stream  produce, 
at  its  juncture  with  the  platinum  electrodes  of  the  aerial,  corre- 
sponding variations  in  the  resistance  of  the  gap.  It  is  of  course 
obvious  that  this  action  produces  corresponding  variations  in  the 
intensity  of  the  radiations.  Numerous  fluids  and  electrolytes  have 
been  employed  by  Marjorana  in  place  of  water.  A  form  of  ionized 
gas  detector  has  been  used  in  connection  with  this  system  with 
excellent  results. 

Fessenden  System.  In  reviewing  the  development  of  radio- 
telephony  it  has  been  necessary  to  refer  so  often  to  the  work  of  Fes- 
senden relative  to  the  many  innovations  introduced  into  the  art  by 
him  that  little  remains  to  be  said  in  this  place  in  regard  to  the  com- 
plete system  which  bears  his  name.  The  bibliography  of  radio- 
telephony  includes  many  papers  and  articles  by  Fessenden  of  the 
greatest  interest  to  the  student  of  wireless  communication.  A  re- 
markably clear  and  concise  paper  on  thp  subject  of  wireless  telephony, 
replete  with  much  valuable  data  on  transmission,  etc.,  was  presented 
by  Prof.  Fessenden  at  the  25th  annual  convention  of  the  American 
Institute  of  Electrical  Engineers  at  Atlantic  City  in  June,  1908. 
Many  illustrations  and  descriptions  of  the  apparatus  employed  by 
him  were  given. 

Among  the  many  interesting  facts  determined  by  Fessenden  in 
his  very  exhaustive  tests  dealing  with  the  atmospheric  absorption 
of  electric  waves,  may  be  mentioned  the  fact  that  waves  of  a  com- 
paratively low  frequency  suffer  less  absorption  than  those  of  a  much 
higher  frequency,  both  being  of  equal  power.  Messages  were  suc- 
cessfully transmitted  in  daylight  with  a  wave-frequency  of  80,000 
per  second  from  Brant  Rock,  Massachusetts,  to  a  radiotelegraphic 
station  in  the  West  Indies — a  distance  of  1,700  miles — with  compara- 
tively little  absorption ;  while  at  the  higher  frequency  of  200,000  per 
second  communication  was  impossible. 

The  power  required  for  radiotelephony,  Fessenden  states  to  be 
about  five  to  fifteen  times  that  required  for  radiotelegraphy.  Fes- 
senden has  employed  at  various  times  all  the  well-known  methods 


112 


WIRELESS  TELEPHONY 


25 


of  generating  a  sustained  train  of  waves  but  has  met  with  greater 
success,  particularly  in  radiotelephony,  by  the  use  of  some  form  of 
the  high-frequency  alternator  method,  shown  in  Figs.  6,  7,  and  12, 
used  in  connection  with  the  heterodyne  receiver  illustrated  in  Fig.  13. 

The  Fessenden  system  has  transmitted  speech  from  Brant 
Rock  to  New  York  City  with  an  expenditure  of  about  200  watts. 
Longer  distances  have  also  been  covered  with  higher  power  apparatus. 
Fessenden 's  patents  are  controlled  by  the  National  Electric  Signaling 
Company. 

DeForest  System.  This  system  is  exploited  by  the  Radio- 
telephone Company  and  is  due  to  Dr.  Lee  DeForest.  It  is  an  oscil- 


AEff/AL 


Pig.  19.     Operating  Circuits  of  the  DeForest  System 

lating  arc  system  presenting  nothing  of  special  novelty.  Fig.  19 
shows  the  essential  features  of  the  operating  circuits,  though  in  prac- 
tice a  more  convenient  means  is  provided  for  facilitating  the  change 
from  the  transmitter  to  receiver.  The  arc  is  of  the  Poulsen  type, 
taking  place  between  a  copper  positive  electrode,  water  cooled,  and 
a  carbon  negative.  An  electromagnetic  means  is  provided  for 
automatically  adjusting  the  length  of  the  arc  by  a  movement  of  the 
carbon  through  the  agency  of  a  solenoid,  which  is  represented  in  the 
drawing  by  the  turns  of  wire  around  the  left-hand  electrode.  A 
variable  resistance  is  employed  to  effect  the  proper  regulation .  of 
this  feature.  The  arc  is  made  to  burn  in  the  flame  of  a  small  alcohol 
lamp.  The  aerial  is  inductively  coupled  to  the  closed  oscillation 
circuit,  the  latter  containing  two  condensers  connected  in  multiple, 


113 


26 


WIRELESS  TELEPHONY 


one  of  which  is  adjustable  for  tuning  purposes.  A  small  incan- 
descent lamp,  connected  to  a  closed  circuit,  is  placed  in  inductive 
relation  with  the  primary  of  the  oscillation  transformer  in  order  to 
give  a  visual  indication  of  the  proper  working  of  the  oscillation  arc. 
The  transformer  used  for  inductive  coupling  with  the  aerial  is  of 
compact  flat  spiral  design,  the  primary  and  secondary  being  placed 
side  by  side  in  a  loose  inductive  couple.  For  telegraphic  and  "call- 
ing" purposes,  a  device  for  rapidly  interrupting  the  steady  flow  of 
waves,  called  a  "chopper,"  is  thrown  in  by  the  movement  of  a  switch; 
whereupon  it  becomes  possible,  by  the  operation  of  the  Morse  key, 
to  cut  up  the  wave-train  into  any  desired  combination  of  dots  and 


Fig.  20.     Circuits  of  the  Collins  System 

dashes.  The  telephone  transmitter,  which  is  introduced  betweer 
the  aerial  and  the  ground,  is  out  of  circuit  during  such  a  performance. 
A  hot-wire  ammeter  is  placed  in  the  aerial  circuit  to  indicate  when 
the  latter  is  in  tune.  For  the  detector,  a  form  of  the  DeForest  audion 
receptor  is  used,  connected  in  the  circuit  as  shown. 

The  DeForest  system  has  met  with  considerable  success,  and 
has  been  installed  on  several  United  States  battleships.  Tests 
have  been  made  with  the  DeForest  equipment  by  the  British  Ad- 
miralty, and  the  greatest  distance  over  which  it  was  possible  to 
transmit  satisfactorily  was  about  57  miles,  a  distance  which  has  since 
been  extended  with  improved  apparatus.  The  sound  from  phono- 
graphic records  transmitted  by  this  system  when  temporarily  in- 
stalled at  the  Eiffel  Tower  in  Paris,  was  said  to  be  audible  400  miles 


114 


WIRELESS  TELEPHONY  27 

away.  This  station  permitted  of  the  use  of  an  exceedingly  tall 
aerial,  the  tower  being  nearly  1,000  feet  high. 

Collins  System.  This  system  has  been  developed  by  A.  F. 
Collins,  who  for  several  years  has  carried  on  experiments  in  the 
field  of  radiotelephony.  The  circuits  employed  are  shown  in  Fig. 
20,  the  arrangement  including  some  unusual  features  though  nothing 
in  the  nature  of  a  radical 
departure.  The  oscillations 
are  created  by  an  arc  of  a 
higher  potential  than  is  gen- 
erally used,  5,000  volts  be- 
ing supplied  through  the 
agency  of  a  direct-current 
dynamo  directly  coupled  to 
a  500-volt  motor.  The  elec- 
trodes of  the  arc  are  both 

in  the  form  of  carbon  disks, .  pig  2l     Oo,Uns  Kevolving  Blectrode8 

which  are  made  to  revolve 

by  means  of  a  small  motor,  as  shown  in  Fig.  21.  A  magnetic  blow- 
out is  also  provided,  the  coils  of  which  serve  the  purpose  of  choke- 
coils,  thus  preventing  the  oscillatory  current  from  entering  the  gener- 
ator. The  aerial  is  of  the  direct-coupled  type  in  both  the  transmit- 
ting and  receiving  stations.  A  visual  indication  of  the  correct  working 
of  the  arc  takes  place  in  the  form  of  a  glow  within  an  exhausted  glass 
tube.  This  tube  is  supplied  with  platinum  terminal  wires  sealed  into 
the  ends,  and  projecting  inwardly  to  within  a  short  distance  from  each 
other.  This  device  is  shunted  across  the  inductance  in  the  closed 
oscillatory  circuit.  The  transmitter  is  located  in  a  local-battery 
circuit  and  acts  inductively  on  a  shunt  connected  across  the  ter- 
minals of  the  arc.  This  shunt  includes  the  secondary  of  the  induc- 
tion coil  and  a  condenser.  Collins  has  recently  employed  several 
transmitters  connected  in  multiple  and  operable  through  a  common 
mouthpiece.  The  detector  employed  in  this  system  is  the  invention 
of  Collins,  and  is  in  effect  a  sensitive  thermo-electric  couple  com- 
posed of  two  dissimilar  metals,  the  juncture  of  which  is  heated  by 
the  received  oscillations.  The  variation  of  this  thermal  effect 
produces  a  corresponding  variation  in  the  effective  resistance 
of  the  detector,  and  consequent  vibrations  of  the  receiver  diaphragm, 


115 


28  WIRELESS  TELEPHONY 

The  Collins  system  is  exploited  by  the  Collins  Wireless  Telephone 
Company  of  Newark,  New  Jersey. 

Conclusion.  In  conclusion  attention  is  called  to  an  important 
characteristic  of  radiotelephonic  communication  which  has  been 
observed  in  practice,  namely,  the  exceptional  clearness  of  articula- 
tion, due  to  an  absence  of  wave-form  distortion  which  is  always 
present  in  wire  telephony  by  reason  of  the  deleterious  effect  of  the 
electrostatic  capacity  of  metallic  lines  and  cables.  This  fact  alone 
bespeaks  wonderful  promise  for  this  form  of  telephony,  particularly 
in  view  of  the  very  limited  distance  over  which  it  is  at  present  possible 
to  telephone  when  the  medium  is  a  submarine  cable. 

Experience  has  thus  far  shown  that  great  advantage  is  to  be 
gained  by  the  very  accurate  tuning  of  the  various  circuits  in  connection 
with  radiotelephony  as  well  as  with  radiotelegraphy.  The  employ- 
ment of  sustained  oscillations  greatly  facilitates  the  accomplishment  of 
more  perfect  resonance;  which,  in  turn,  tends  to  eliminate  interference 
and  aids  selective  communication.  Experience  has  also  shown  that 
in  systems  using  an  inductively  coupled  aerial,  a  decided  gain  in  the 
clearness  of  articulation  is  noticeable  when  such  coupling  is  " loose." 
In  practice,  therefore,  the  primary  and  secondary  helices  are  often 
separated  several  inches. 

In  the  foregoing  discussion  of  radiotelephony  it  has  been  impos- 
sible to  do  more  than  very  briefly  present  the  subject.  Many  in- 
teresting questions  of  a  theoretical  nature  and  a  description  of  several 
other  systems,  it  has  been  found  necessary  to  omit.  If,  however,  the 
present  short  survey  awakens  a  greater  interest  in  space-communica- 
tion, the  reader  may  avail  himself  of  the  extensive  literature  dealing 
with  the  subject,  and  delve  as  deeply  into  the  theory  and  problem* 
involved  as  he  desires. 


116 


WIRELESS  TELEGRAPHY  IN 
AERONAUTICS 


WIRELESS  ON  DIRIGIBLES 

Early  Experiments  on  Balloons.  It  will  be  apparent  that  one  of 
the  most  valuable  features  of  the  use  of  the  dirigible  and  the  aero- 
plane in  warfare  is  the  possibility  of  communicating  with  headquar- 
ters by  wireless  telegraphy,  which  means  the  instant  reception  of 
information  gained  by  scouting  parties.  Not  long  after  the  inven- 
tion of  sending  messages  through  the  air  became  a  reality,  Professor 
Slaby  demonstrated  that  wireless  signals  emitted  by  a  land  station 
can  be  received  by  a  balloon,  floating  freely  in  the  air.  The  experi- 
ments were  carried  out  in  conjunction  with  the  maneuvers  of  the 
Prussian  balloon  corps,  and  since  then  experiments  have  been  made 
successfully  in  other  countries.  The  balloon  Condor,  which  made 
an  ascension  near  Brussels,  in  the  latter  part  of  1909,  maintained 
uninterrupted  communication  with  the  station  on  the  Brussels 
Palais  de  Justice,  and  also  caught  signals  sent  from  the  Eiffel  Tower 
at  Paris,  180  miles  distant.  Prior  to  this,  Professor  Hergesell  had 
already  demonstrated  the  great  value  of  the  application  of  wireless 
telegraphy  to  balloons  by  controlling  the  valves  of  unmanned  sound- 
ing balloons  (small  balloons  sent  aloft  for  the  purpose  of  carrying 
meteorological  instruments),  at  heights  extending  to  ten  miles,  by 
wireless  impulses.  The  receivers  of  the  balloons  were  tuned  to 
different  wave  lengths,  so  that  the  valve  of  any  one  balloon  could  be 
opened  and  that  particular  balloon  brought  down  at  will. 

In  a  series  of  experiments  made  with  the  German  military  bal- 
loon Gross  II,  in  the  autumn  of  1908,  messages  were  sucessfully 
sent  from,  as  well  as  to,  the  airship,  the  first  balloon  wireless  stations 
being  constructed  according  to  the  Telefunken  system.  It  was 
proved  by  preliminary  experiments  in  the  balloon  shed  that  the  dan- 
ger of  igniting  the  contents  of  the  gas  bag  by  sparks  emitted  from  the 
wireless  apparatus  could  be  averted  by  taking  suitable  precautions. 


119 


.2         WIRELESS   TELEGRAPHY  IN  AERONAUTICS 

This  danger  is  least  with  airships  of  the  flexible  and  semi-rigid  types, 
in  which  the  gas  bag  possesses  very  few  metallic  parts  that  could 
draw  sparks  from  the  highly  charged  aerial  which  is  used  for  sending 
and  receiving  the  flashes  from  the  air.  The  suspension  of  the  car  of 
the  Gross  by  hempen  ropes  insured  the  complete  insulation  of  the 
electrical  apparatus  from  the  gas  bag,  and  all  parts  at  which  sparks 
were  formed  were  enclosed  in  gas-tight  envelopes.  For  military 
reasons,  the  details  of  these  experiments  were  not  made  public,  but 
the  results  are  said  to  have  been  very  satisfactory. 

These  experiments  have  proved  that  electro-magnetic  waves 
are  propagated  to  great  heights  in  the  atmosphere  and  that  the  part 
played  by  the  earth  in  wireless  telegraphy  is  far  less  important  than 
has  been  assumed.  Thus,  one  of  the  principal  theoretical  objections 
to  the  application  of  wireless  to  airships  has  been  shown  to  be  falla- 
cious. In  the  German  army  maneuvers  of  1909,  the  Gross  II  demon- 
strated, for  the  first  time,  the  practical  utility  of  wireless  teleg- 
raphy on  a  scouting  balloon.  The  Zeppelin  airship  which  took  part 
in  the  maneuvers  did  not  possess  this  advantage.  Subsequently 
the  Zeppelin  III  was  equipped  with  wireless  apparatus  and  it  was 
shown  that  even  with  a  rigid,  metallic-framed  airship  of  this  type, 
wireless  signals  could  be  transmitted  with  safety  to  a  distance  of  300 
miles  or  more.  All  of  the  later  Zeppelin  airships  which  have  since 
been  wrecked,  and  particularly  the  passenger-carrying  types,  were 
equipped  with  wireless. 

Dangers  from  Electric  Discharge.  While  of  inestimable  advan- 
tage, the  presence  of  the  wireless  apparatus  on  a  metallic  airship 
exposes  it  to  new  dangers,  some  of  which  are  also  present  in  the  case 
of  the  aeroplane.  The  chief  source  of  risk  is  the  large  volume  of 
inflammable  gas  necessary  for  flotation  in  the  case  of  the  huge  diri- 
gibles. In  a  thunder  storm,  a  balloon  is  subject  to  sudden  varia- 
tions of  electric  charge  which  may  produce  sparks  capable  of  ignit- 
ing its  contents.  Wireless  signals  are  accompanied  by  equally  great 
and  rapid  changes  of  potential  which  may  produce  the  same  result. 

It  seems  probable  that  the  destruction  of  the  Zeppelin  airship 
at  Echterdingen  was  due  to  atmospheric  electric  discharges  during 
a  thunder  storm,  while  the  catastrophe  which  befell  the  French  mili- 
tary dirigible  La  Republique  in  September,  1909,  also  appears  to 
have  been  due  indirectly  to  an  electric  spark.  A  hole  was  torn  in 


120 


WIRELESS   TELEGRAPHY  IN  AERONAUTICS        3 

the  gas  bag  by  the  breaking  of  a  propeller  blade,  which  in  itself  would 
not  have  been  sufficient  to  have  caused  the  sudden  drop  of  300  feet. 
It  is  a  well-known  fact  that  gas  or  steam,  escaping  rapidly  from  an 
orifice,  will  acquire  an  electric  charge  which  may  produce  powerful 
sparks,  and  it  is  thought  that  this  took  place  immediately  follow- 
ing the  rupture  of  the  gas  bag  of  the  Republique,  setting  its  contents 
on  fire. 

As  the  gas  can  not  be  ignited  by  discharges  from  the  envelope 
itself,  the  netting,  ropes,  and  similar  poor  conductors  (unless  they 
become  saturated  with  water),  but  can  be  easily  set  fire  to  by  sparks 
from  the  metal  parts  of  the  valve  and  other  masses  of  metal,  it  is 
obvious  that  all  metal  and  other  good  conductors  will  have  to  be 
eliminated  from  the  envelope.  There  seems  to  be  no  objection  to 
the  presence  of  metal  in  the  car,  while  a  well-conducting  drag  rope 
is  a  safeguard  against  explosion  in  landing.  If  all  conductors  are 
removed  from  the  vicinity  of  the  gas  bag,  there  would  appear  to  be 
no  danger  in  the  application  of  wireless  telegraphy  to  airships  of  the 
flexible  type.  If  the  same  precautions  be  taken,  dirigibles  of  this 
class  are  no  more  liable  to  ignition  by  atmospheric  electrical  dis- 
charges than  the  free  balloon. 

In  rigid  airships  with  metallic  frames,  the  conditions  are  totally 
different.  It  will  be  apparent  in  the  Zeppelin  type,  with  its  alumi- 
num frame  and  its  numerous  gas  bags  filled  with  hydrogen,  every 
condition  of  easy  ignition  is  present.  Between  the  great  cylindrical 
conducting  frame,  which  is  more  than  400  feet  long  and  40  feet  in 
diameter,  and  the  surrounding  air,  there  may  exist  a  difference  of 
potential  of  65,000  volts  when  the  airship  is  horizontal,  and  of  50,000 
volts,  when  steeply  inclined.  A  spark  capable  of  causing  ignition 
may  be  caused  by  a  difference  of  potential  of  only  3,000  volts.  As 
it  does  not  appear  to  be  practicable  to  substitute  wood  for  the  alumi- 
num framing,  Zehnder  recommends  protection  of  airship  by  light- 
ning rods  projecting  beyond  the  reach  of  escaping  gas,  He  also 
suggests  making  the  gas  container  of  sheet  metal,  the  stiffness  of 
which  might  make  it  possible  to  employ  a  lighter  skeleton,  thus  keep- 
ing the  weight  within  the  same  limit  as  at  present.  No  electrical 
discharge  could  take  place  within  this  metallic  envelope  and  the 
induced  surface  charge  would  escape  harmlessly  into  the  atmosphere 
from  projecting  seams  and  points.  As  an  additional  precaution, 


121 


4         WIRELESS  TELEGRAPHY  IN   AERONAUTICS 

the  aluminum  cars  could  be  connected  with  the  aluminum  balloon 
at  several  points  by  a  number  of  wires,  so  that  the  aeronauts  would 
be  enclosed  in  a  sort  of  Faraday's  cage,  protecting  them  from  exter- 
nal electrical  influences. 

Preventive  Methods.  The  experiments  of  Professor  Wiener 
have  not  only  served  to  demonstrate  the  value  of  a  wire  cage  as 
protection  against  electrical  discharges,  but  likewise  have  illustrated 
what  happened  to  a  balloon  when  struck  by  a  spark.  For  this  pur- 
pose, a  model  balloon  was  suspended  above  a  large  induction  coil 
with  the  gaps  of  the  secondary  so  arranged  that  the  largest  diameter 
of  the  balloon  was  between  one  pair,  while  a  second  pair  was  located 
to  discharge  immediately  below  the  valve  opening  of  the  balloon. 
When  a  spark  was  passed  completely  through  a  collodion  balloon, 
filled  with  either  hydrogen  or  illuminating  gas,  the  gas  ignited  with- 
out explosion  so  that  the  balloon  was  quietly  consumed.  It  is  only 
when  the  balloon  contains  air  mixed  with  gas  that  explosion  takes 
place.  A  balloon  can  even  be  traversed  by  sparks  without  being 
ignited.  Metzeler  has  recently  introduced  a  balloon  material  com- 
posed largely  of  aluminum  for  the  purpose  of  protecting  the  gas  from 
the  sun's  rays,  but  experiments  prove  that  this  material  is  no  better 
conductor  than  the  ordinary  balloon  fabric.  Sparks  can  be  passed 
through  a  balloon  of  Metzeler's  material  without  causing  ignition 
and  even  collodion  balloons  can  transmit  a  few  sparks  without  burn- 
ing. If  the  flow  of  sparks  be  so  rapid  and  dense  as  to  resemble  a 
flaming  arc,  it  may  directly  ignite  the  fabric.  Even  if  it  were  pos- 
sible to  make  a  balloon  of  conducting  material,  it  would  still  be 
desirable  to  surround  it  with  a  wire  cage,  as  lightning  naturally  fol- 
lows the  shortest  path.  With  this  provision,  the  conductivity  of 
the  balloon  is  of  no  importance.  Owing  to  its  greater  strength  the 
wire  netting  need  not  be  heavier  than  the  hemp  netting  ordinarily 
employed  on  dirigibles  of  the  flexible  and  semi-flexible  types.  All 
the  experiments  just  referred  to  were  made  with  unprotected  bal- 
loons, but  a  model  surrounded  by  a  wire  cage  allowed  ordinary  sparks 
to  pass  indefinitely,  while  it  also  withstood  a  flaming  arc  for  a  short 
time,  without  igniting.  Fifteen  seconds  direct  contact  with  the 
flame  was  necessary  to  produce  ignition.  The  ropes  supporting 
the  car  must  also  be  of  wire  and  must,  completely  surround  the  car. 
It  might  be  supposed  that  making  the  outside  of  the  balloon  a  good 


122 


WIRELESS   TELEGRAPHY   IN   AERONAUTICS          5 

conductor  would  rather  invite  danger  from  lightning,  but  this  is  not 
the  case.  Although  the  ordinary  balloon  envelope  is  a  fairly  good 
insulator  against  low  voltages,  it  is  unable  to  resist  the  high  tension 
of  atmospheric  electricity.  An  electroscope  charged  to  2,000  volts 
is  discharged  in  less  than  a  second,  when  it  is  touched  with  a  roll 
of  balloon  fabric  about  six  inches  long.  Hence,  the  balloon  increases 
the  electrical  tension  immediately  above  and  below  it,  as  much  as 
it  would  do  if  it  were  a  perfect  conductor,  but  when  the  discharge 
occurs,  its  destructive  action  will  be  greater  in  proportion  to  the 
electrical  resistance  opposed  to  it.  It  might  also  be  objected  that 
the  Faraday's  cage  would  prove  a  source  of  danger  to  the  occupants. 
The  discharge,  however,  passes  chiefly  through  the  wires,  and  only 
partial  or  inductive  discharges  can  strike  those  in  the  balloon.  It 
is  evident  that  the  Faraday's  cage  is  quite  as  readily  applicable  to  the 
aeroplane  as  it  is  to  the  dirigible,  through  its  use  might  complicate  the 
employment  of  the  aerial  for  wireless  telegraphy,  as  referred  to  later. 

On  the  other  hand,  it  is  quite  possible  that  the  surrounding  net- 
work of  wire  might  be  employed  for  both  purposes  by  suitably  pro- 
tecting the  instruments.  But  even  when  a  balloon  is  thus  pro- 
tected from  lightning,  it  is  exposed  to  another  danger,  atmospheric 
electricity.  A  balloon  has  been  ignited  and  consumed  by  small 
sparks  produced  by  touching  the  escape  valve  after  landing.  This 
valve  and  the  filling  tube,  normally  open  during  flight,  are  the  two 
places  in  which  the  gas  can  come  into  contact  with  the  air  and  there- 
fore need  special  protection.  The  simple  and  long-known  device 
employed  in  the  Davy  safety  miner's  lamp  can  well  be  employed  for 
this  purpose.  These  safety  lamps  are  designed  to  protect  miners 
from  explosions  of  fire  damp,  the  flame  being  surrounded  by  a  fine 
wire  netting  which  conducts  heat  so  well  that  the  temperature 
required  to  ignite  the  gas  can  not  be  produced  on  the  outside.  Any 
gas  which  enters  the  lamp  burns  quietly  without  producing  an  explo- 
sion. Both  the  escape  valve  and  filling  tube  of  the  balloon  could  be 
surrounded  with  a  fine  netting  of  copper  wire,  which  would  also 
afford  protection  from  lightning  in  certain  cases. 

An  electric  discharge  may  be  precipitated  by  pulling  the  valve 
cord  in  a  strong  electric  field,  as,  according  to  Paschen's  experiments, 
the  gap  that  a  certain  tension  will  bridge  is  greater  in  hydrogen  than 
in  air.  This  is  shown  by  connecting  a  Bunsen  burner  with  one 


123 


6         WIRELESS   TELEGRAPHY   IN  AERONAUTICS 

pipe  of  an  induction  coil  and  gradually  raising  the  other  above  it  until 
the  opening  is  too  great  for  the  sparks  to  bridge.  Upon  turning  on 
the  gas,  the  flow  of  sparks  will  recommence.  If  the  burner  be  sur- 
rounded with  a  wire  netting,  the  gas  will  burn  only  on  the  outside. 
The  experiments  with  the  model  balloons  and  a  large  induction  coil 
showed  that  when  the  sparks  passed  beneath  the  open  filling  tube  of 
the  balloon,  ignition  sometimes  followed,  but  where  protected  by 
a  wire  netting,  a  flaming  arc  playing  upon  the  netting  for  a  minute 
did  not  light  the  gas. 

Wireless  on  the  Zeppelins.  In  regard  to  the  employment  of 
wireless  telegraphy  on  the  Zeppelin  type  of  the  present  form — an 
arrangement  of  the  aerial  which  would  minimize  the  danger  of  igni- 
tion and  would  also  furnish  the  best  electrical  conditions  for  the 
transmission  of  signals,  is  suggested;  as  the  hull  of  the  Zeppelin  is 
traversed  by  a  vertical  shaft  or  well,  it  is  possible  to  support  the 
aerial  by  a  simple  Eddy  kite,  which  would  be  kept  aloft  by  the  motion 
of  the  airship.  The  wireless  apparatus,  including  the  dynamo,  would 
be  housed  in  the  middle  of  the  runway  which  connects  the  two  cars. 
The  kite  would  be  connected  with  the  apparatus  by  a  wire  from  600 
to  1,200  feet  in  length,  i.  e.,  one-fourth  to  one-fifth  the  length  of  the 
electric  waves  employed.  A  second  wire  of  the  same  length  and 
carrying  a  weight  at  its  end  would  hang  downward  from  the  appara- 
tus and  would  be  kept  as  nearly  vertical  as  possible  by  insulated 
stay  or  guy  lines  attached  to  the  cars.  The  lower  wire  might, 
however,  be  replaced  by  a  fan-shaped  antenna  about  200  feet  long, 
attached  to  the  frame  of  the  airship  and  projecting  about  30  feet 
below  the  hull.  With  this  arrangement  communication  would  be 
possible  even  when  the  ship  was  flying  low.  Fouling  of  the  propel- 
lers would  have  to  be  guarded  against  by  enclosing  them  in  wire 
baskets  or  housings. 

The  T-shaped  antenna  which  is  carried  by  ships  using  the  Tele- 
f unken  system,  could  also  be  applied  without  difficulty  to  the  Zeppe- 
lin airship,  as  the  metal  frame  is  abundantly  able  to  carry  a  light, 
hollow  mast  about  30  feet  high,  which  could  be  raised  and  lowered 
by  ropes.  The  stability  of  the  airship,  however,  would  be  affected 
more  by  this  complicated  device  than  by  the  kite.  Experiments 
have  shown  conclusively  the  great  promise  of  the  use  of  wireless  teleg- 
raphy on  airships,  but  an  indispensable  prerequisite  to  its  adoption 


124 


WIRELESS  TELEGRAPHY  IN  AERONAUTICS         7 

would  appear  to  be  the  electro-technical  development  of  means  of 
protection  from  all  danger  of  injury  through  the  working  of  the  appa- 
ratus itself,  or  from  atmospheric  electricity. 

WIRELESS  ON  AEROPLANES 

Owing  to  its  far  greater  speed  and  radius  of  action  as  well  as  its 
more  general  availability,  the  employment  of  wireless  telegraphy 
on  the  aeroplane  holds  far  more  promise  for  military  use.  With 
experience  in  taking  observations  from  a  height  it  will  become  pos- 
sible to  plot  maps,  note  the  character  of  emplacements,  and  the  posi- 
tion of  troops  from  an  altitude  that  would  make  danger  from  shell 
fire  from  below  out  of  the  question.  To  be  of  any  value,  the  diri- 
gible must  be  so  large  as  to  make  this  impossible. 

First  Message.  To  James  McCurdy,  one  of  the  Curtiss  school 
aviators,  belongs  the  distinction  of  having  been  the  first  to  communi- 
cate by  wireless  from  an  aeroplane  to  a  land  station.  This  was  on 
August  27,  1910,  when  he  sent  the  following  message  from  a  Curtiss 
biplane : 

Over  Barren  Island,  N.  Y.,  6:45  P.  M.,  Aug.  27,  '10. 
To  H.  M.  HORTON: 

Another  chapter  in  aerial  achievement  is  recorded  in  the  sending  of  this 
wireless  message  from  an  aeroplane  in  flight.  McCuKDY. 

Horton  was  the  wireless  operator  on  the  roof  of  the  Sheepshead 
Bay  race-track  grand  stand,  two  or  three  miles  distant  from  Bar- 
ren Island,  though  the  distance  was  probably  less  in  an  airline.  The 
apparatus  was  an  ingenious  makeshift  merely  intended  for  the  pur- 
pose of  sending  and  was  not  capable  of  receiving  a  message.  It  was 
extremely  compact,  the  complete  outfit,  with  the  exception  of  the 
battery,  being  attached  to  the  steering  wheel  of  the  aeroplane.  The 
battery  was  carried  in  the  aviator's  vest  pocket,  while  the  aerial 
consisted  of  50  feet  of  ordinary  wire  held  straight  by  a  small  lead 
weight,  the  whole  trailing  after  the  machine  in  flight.  Such  an  out- 
fit naturally  had  but  a  very  limited  range,  probably  not  more  than  five 
miles,  owing  to  the  small  amount  of  energy  available,  and  would  be 
subject  to  destructive  interference  from  the  waves  sent  out  by  more 
powerful  stations  in  its  vicinity.  It  was  intended  only  to  demon- 
strate the  possibility  of  communicating  with  an  aeroplane  in  flight. 


125 


8         WIRELESS   TELEGRAPHY   IN   AERONAUTICS 

Owing  to  the  high  speed  at  which  an  aeronautic  motor  runs,  how- 
ever, it  would  be  practical  to  carry  a  very  compact  alternating  gener- 
ator which  would  weigh  very  little  and  still  give  the  aeroplane  send- 
ing station  a  comparatively  wide  radius  of  action — doubtless  up  to 
100  miles  or  more,  due  to  the  greater  facility  with  which  the  electro- 
magnetic waves  can  be  transmitted  from  a  height.  The  remainder 
of  the  apparatus  could  likewise  be  made  in  very  compact  and  durable 
form,  so  that  there  would  appear  to  be  no  "wireless  problem"  where 
the  aeroplane  is  concerned — it  is  merely  a  matter  of  designing  instru- 
ments for  the  purpose. 

Morton's  Experiments.  The  question  of  equipping  the  aero- 
plane with  a  suitable  aerial  that  would  be  effective  without  being  an 
encumbrance,  as  well  as  the  fact  that  a  very  substantial  percentage 
of  the  energy  emitted  by  the  sending  apparatus  was  absorbed  by 
the  numerous  guy  wires  which  also  acted  as  a  shield  to  the  antennae, 
appeared  to  present  a  difficult  obstacle  at  first.  Both,  however,  have 
been  overcome  by  a  very  simple  expedient,  that  of  employing  the 
guy  wires  themselves  as  the  antennae.  After  experimenting  for  a 
long  while  with  numerous  different  methods  of  stringing  separate 
antennae,  H.  M.  Horton  hit  upon  the  idea  of  using  the  wires  for 
this  purpose,  while  the  motor  is  utilized  as  a  ground.  Experiments 
which  were  made  with  a  machine  thus  equipped  and  located  in  the 
building  of  the  United  States  Aeronautical  Reserve  in  New  York 
City,  proved  most  successful.  Messages  were  received  from  vari- 
ous stations  throughout  the  city  and  even  from  ships  at  sea,  despite 
the  fact  that  the  aeroplane  was  located  on  the  first  floor  of  the  build- 
ing and  was  not  connected  with  any  form  of  antennae  protruding 
above  the  roof.  A  very  light  equipment  was  used,  the  total  weight 
not  exceeding  65  pounds,  although  a  6-inch  spark  coil  was  employed. 
Energy  is  derived  from  a  12-volt  storage  battery  with  a  50-ampere- 
hour  capacity,  the  six  cells  weighing  but  40  pounds.  The  guy  wires 
are  connected  in  series  and  give  a  total  length  of  800  feet  on  the 
machine  in  question.  However,  the  employment  of  a  storage  bat- 
tery in  this  connection  can  be  considered  only  as  a  tempory  expe- 
dient, in  view  of  the  obvious  limitations  of  such  a  source  of  energy. 
For  extended  practical  use,  a  generator  would  be  necessary.  As 
the  required  power  is  right  at  hand,  this  could  take  the  form  of 
a  small  high-frequency  alternator,  and  as  this  could  be  wound  for  a 


126 


WIRELESS   TELEGRAPHY  IN  AERONAUTICS 


9 


high  voltage,  the  weight  of  the  transformer  necessary  could  be  cor- 
respondingly reduced. 

Recent  Records.  Lorraine.  Numerous  other  experimenters 
have  been  at  work  with  wireless  during  the  past  year  or  so,  Robert 
Lorraine,  in  England,  having  succeeded  in  maintaining  perfect 
communication  from  his  aeroplane  with  a  land  station  more  than 
a  mile  distant. 

Beck.  The  most  practical  results,  however,  were  those  of  the 
trials  carried  out  during  the  course  of  the  aviation  meet  at  San 


Fig.  1.    Parmalee  and  Lieutenant  Beck  in  a  Wright  Biplane,  Operating 
a  Wireless  Outfit 

Francisco  in  January,  1911.  Lieutenant  Paul  W.  Beck  of  the  United 
States  Signal  Corps  went  aloft  in  a  Wright  biplane  piloted  by  Parm- 
alee, Fig.  1,  and  transmitted  wireless  messages  for  a  considerable 
distance  while  at  a  height  of  1,000  feet.  These  messages  were 
received  at  the  Mare  Island  Navy  Yard,  40  miles  away,  as  well  as 
at  the  Yerba  Buena  Island  training  school  in  San  Francisco  Bay. 
In  Lieutenant  Beck's  experiments  a  100-foot  length  of  copper  wire 
was  trailed  along  behind  the  aeroplane.  In  France,  wireless  mes- 
sages have  been  transmitted  15  miles  from  an  aeroplane  success- 
fully, while  in  England,  during  a  trip  of  the  military  dirigible 


127 


J 


10       WIRELESS   TELEGRAPHY  IN  AERONAUTICS 

Beta,  communication  was  established  with  headquarters,  30  miles 
distant. 

McCurdy.  During  the  Bridgeport,  Connecticut,  Aviation  Meet 
in  May,  1911,  McCurdy  set  a  new  long-distance  mark  in  wireless 
communication  from  an  aeroplane  by  sending  messages  to  the  opera- 
tor in  the  dome  of  the  World  Building  in  New  York  City,  55  miles 
distant,  while  a  number  of  other  stations  within  a  shorter  radius 
also  picked  up  his  messages.  The  apparatus  was  constructed  for 
the  New  York  World  in  three  days  by  Oscar  Roesen,  an  electrical 
engineering  student  at  Stevens,  and  was  probably  the  first  set  capable 
of  both  sending  and  receiving  that  has  been  mounted  on  an  aero- 
plane. The  transmitter  consisted  of  a  4-inch  induction  coil  of  the 


Fig.  2.    Diagram  Showing  Method  of  Making  an  Aerial  on  a  Biplane 

ordinary  vibrating  type,  supplied  with  current  by  15  dry  cells  con- 
nec^ed  in  series,  thus  giving  a  voltage  of  22.5,  while  the  amperage 
was  high.  The  helix  was  a  wood  frame  5  inches  in  diameter  and 
wound  with  12  turns  of  No.  6  B  &  S  gauge  aluminum  wire,  while  the 
condenser  consisted  of  copper  plates  with  a  special  insulating  material 
as  the  dielectric.  An  ordinary  telegraph  key  was  employed.  The 
receiver  comprised  a  mineral  detector,  two  straight  tuning  coils,  and 
a  pair  of  2,000-ohm  head  phones.  The  aerial  consisted  of  a  series 
of  wire  strung  forward  from  the  tail  on  either  side  to  points  directly 
above  the  ailerons  at  the  ends  of  the  upper  plane  of  the  Curtiss 
machine,  Fig.  2.  For  a  ground,  or  rather  for  a  balancing  aerial, 


128 


WIRELESS   TELEGRAPHY  IN  AERONAUTICS        11 

the  motor,  supplemented  by  wires  carried  out  in  either  direction 
to  the  ends  of  the  main  plane,  was  employed.  The  apparatus 
proper  was  mounted  in  a  small  box  carried  below  the  aviator  on  the 
skids  of  the  machine,  while  the  sending  key  was  placed  on  the  steer- 
ing wheel.  The  arrangement  is  plainly  illustrated  by  the  accompany- 
ing sketch,  Fig  3.  A  is  the  box,  B  the  key,  dotted  lines  C  the 
ground  or  balancing  aerial,  and  full  lines  CC  the  aerial  proper.  The 
weight  of  the  outfit  was  between  40  and  50  pounds.  Lieutenant 
Fickel,  U.  S.  A.,  detailed  by  the  War  Department  to  attend  the 
meet,  was  very  much  impressed  with  the  set  and  sent  a  complete 
description  of  it  to  the  Signal  Corps  at  Washington.  Experiments 
were  first  made  on  ay  Saturday,  and  while  McCurdy's  signals  were 


Fig.  3.    Diagram  Showing  Location  of  Circuits  and  Equipment  of  a 
Wireless  Outfit 

plainly  heard  at  the  temporary  receiving  station  on  the  field,  the 
interference  of  numerous  adjacent  stations  made  it  impossible  for 
the  operator  in  New  York  to  pick  them  up.  On  the  following  day, 
there  was  an  absence  of  interference,  and  the  messages  were  plainly 
heard  in  New  York  on  three  different  trials,  thus  establishing  a  new 
distant  record  for  aeroplane  work,  and  this  is  of  even  greater  impor- 
tance in  having  reached  the  heart  of  the  metropolis,  as  New  York 
City  is  generally  conceded  to  have  many  adverse  elements  for  suc- 
cessful wireless  .reception  from  outside  points,  chiefly  due  to  the 
great  number  of  high,  steel-frame  buildings.  Tests  which  were 
made  of  the  receiving  abilities  of  the  set  showed  that  it  was  abund- 
antly capable  of  picking  up  messages  from  a  distance  of  200  miles, 
but,  unfortunately,  no  actual  trials  of  this  nature  were  carried  out 
in  the  air. 


129 


12        WIRELESS   TELEGRAPHY   IN   AERONAUTICS 

General  Problems.  It  will  be  apparent  from  the  foregoing 
that  all  of  the  experiments  made  thus  far  have  been  in  transmitting 
messages  from  an  aeroplane  in  flight,  and  while  this  is  a  very  val- 
uable accomplishment,  receiving  is  quite  as  necessary,  to  take  com- 
plete advantage  of  the  value  of  the  wireless  as  a  means  of  communica- 
tion, and  for  reasons  that  are  obvious  this  does  present  more  of  a 
problem  than  the  mere  sending  of  messages. 

Eliminating  Noise.  The  chief  difficulty  is  that  of  noise,  as 
with  the  unmuffled  motors  now  generally  in  use,  it  is  practically 
impossible  for  two  men  sitting  side  by  side  in  an  aeroplane  to  carry 
on  a  conversation.  This  is  further  complicated  by  the  rush  of  the 
wind  and  the  high  pitched  note  occasioned  by  the  vibration  of  the 
numerous  guy  wires  and  struts,  but  with  close-fitting,  double-head 
receivers,  there  should  be  no  difficulty  in  shutting  out  practically 
everything  but  the  noise  of  the  motor.  The  matter  of  expediency 
that  has  been  responsible  for  the  adoption  of  so  many  of  the  make- 
shift features  of  design  that  characterize  the  present-day  aeroplane, 
and  probably  will  continue  to  do,  at  least  for  a  few  years  to  come, 
has  likewise  been  responsible  for  the  elimination  of  the  muffler  on 
the  motor.  But  even  now,  design  and  construction  have  advanced 
to  a  point  where  there  is  really  no  necessity  for  longer  doing  without 
this  essential,  as  both  the  muffler  and  its  connecting  pipe  can  readily 
be  made  of  aluminum,  though,  for  that  matter,  the  weight  of  the 
standard  type  as  employed  on  the  automobile  would  not  form  any 
very  serious  drawback.  Considerably  more  difficulty  would  be 
encountered  in  muffling  motors  of  the  rotary  type,  but  they  need 
it  least,  as  the  explosions  of  a  seven-  or  fourteen-cylinder  Gnome 
motor  running  at  full  speed  overlap  to  a  degree  that  converts  the 
exhaust  into  a  loud  buzz,  rather  than  the  disagreeable  and  ear- 
cracking  rapid-fire  bang  of  the  four-  or  six-cylinder  vertical  motor. 

Use  of  Visible  Signals.  Should  the  usual  audible  method  of 
receiving  not  prove  practical,  two  alternatives  are  open,  both  involv- 
ing the  use  of  a  visible  signal.  In  one,  a  coherer  could  be  connected 
with  a  tuning  condenser  shunted  across  it,  the  former  being  auto- 
matically decohered  every  two  seconds  by  a  striker  actuated  by  a 
magnet  excited  by  a  clockwork  contact  maker.  A  relay  and  bat- 
tery are  connected  in  series  with  the  coherer,  and  the  local  circuit 
of  the  relay  is  connected  with  another  battery  and  small  incandes- 


130 


WIRELESS   TELEGRAPHY   IN   AERONAUTICS        13 

cent  lamp.  Each  time  a  signal  is  received  the  lamp  would  light- 
one  second  for  a  dot  and  two  seconds  for  a  dash.  These  long  signals 
are  obviously  necessary,  but  in  spite  of  that  a  message  could  be 
received  with  reasonable  rapidity.  The  second  alternative  is  that 
of  employing  an  inker,  this  method  also  involving  the  use  of  a  coherer. 
The  inking  apparatus,  however,  is  not  only  comparatively  heavy, 
but  in  order  to  work  satisfactorily,  requires  fairly  close  adjustment, 
so  that  it  would  not  be  suitable  for  use  where  there  is  much  vibration. 
The  question  of  vibration  is  probably  the  most  serious  element  of 
the  problem.  The  coherer  is  not  a  particularly  sensitive  receiver  of 
the  weak  impulses  which  have  to  be  caught,  and  has  long  since  been 
practically  abandoned  in  wireless  practice.  But  even  if  it  were  suf- 
ficiently sensitive  for  such  use,  it  would  probably  be  impossible  to 
make  the  coherer  work  long  enough  to  start  the  local  side  of  the 
relay  working  effectively,  particularly  if  the  mechanical  decohe- 
sion  had  to  be  rapid.  In  fact,  the  actual  number  of  impulses  per 
second  of  a  four-cylinder,  two-cycle  engine,  or  a  six-cylinder,  four- 
cycle, or  any  of  the  rotary  motors,  is  too  great  to  permit  a  coherer 
to  act,  while  a  coherer  insensitive  to  the  abruptness  of  the  shock 
would  not  be  sensitive  enough  to  respond  to  the  wireless  impulses. 
Either  the  mineral  or  the  electrolytic  type  of  detector  is  far  more 
sensitive,  but  as  its  adjustment  must  be  delicate  to  work  effectively, 
it  would  also  be  placed  at  a  serious  disadvantage  by  the  vibration. 

Forms  of  Aerial.  The  question  of  the  most  practical  form  of 
aerial  to  employ  is  another  difficulty  that  affects  both  sending  and 
receiving.  The  use  of  a  long  trailing  wire,  as  well  as  the  employ- 
ment of  the  network  of  guys  and  braces,  has  already  been  referred 
to  in  connection  with  experiments  carried  out  by  McCurdy  and 
American  army  officers.  Trailing  wires  present  so  many  sources  of 
danger  to  a  machine  traveling  at  high  speed,  that  few  pilots  would 
care  to  consent  to  their  use,  while  connecting  up  the  bracing  of  the 
aeroplane  is  equally  impracticable  as  every  piece  of  metal  on  the 
machine  then  becomes  charged,  and  in  sending,  serious  shocks  might 
be  received  by  the  pilot  or  his  passenger.  Farman  has  employed 
two  trailing  wires,  each  about  400  feet  long,  and  Baker  has  adapted 
a  similar  arrangement  to  a  Bristol  biplane  in  England,  the  wires, 
however,  not  being  allowed  to  hang  loose  in  the  latter  case,  thus  lim- 
iting their  capacity.  Instead  of  using  balanced  aerials,  as  in  the 


131 


14       WIRELESS   TELEGRAPHY  IN  AERONAUTICS 

McCurdy  experiments  described  above,  he  coupled  them  to  each  end 
of  an  inductance  coil,  thus  increasing  their  effective  length  to  the 
greatest  extent  possible  without  sacrificing  their  efficiency.  The 
apparatus  consisted  of  a  6-inch  induction  coil  with  a  %-inch  spark 
gap  located  as  far  away  from  the  gasoline  tank  as  possible.  Two 
light  brass  rods  extended  from  the  coil  well  into  the  space  between 
the  two  main  planes  of  the  machine  and  to  one  side  of  the  tank,  and 
two  ^-inch  rods  sliding  on  these  and  with  their  ends  separated  by 
%  inch,  formed  the  spark  gap  terminals.  Shunted  across  the  spark 
gap  was  a  condenser  of  the  Ley  den  jar  type,  and  an  inductance  coil 
consisting  of  seven  turns  of  No.  14  copper  wire  wound  on  a  light 
ebonite  drum.  This  inductance  had  sliding  contacts  so  that  the 
number  of  turns  used  could  be  varied  in  the  usual  manner,  in  order 
to  tune  the  two  circuits.  The  two  aerial  wires  were  connected  to  the 
two  ends  of  the  inductance  in  use  and  the  aerial  circuit  was  brought 
into  tune  with  the  shunt  circuit.  A  storage  battery  of  five  cells 
supplied  the  necessary  energy,  about  50  to  60  watts  being  required. 
Two  new  arrangements  which  should  greatly  increase  the  efficiency 
of  the  apparatus  have  since  been  adopted.  The  more  important  of 
these  is  a  long,  light  brass  tube  attached  to  the  tail  of  the  aeroplane 
but  insulated  from  it.  This  acts  as  counter-capacity  or  "ground" 
to  a  long  aerial  wire  on  the  other  side.  This  aerial  starts  from  the 
nose  of  the  machine,  and  is  carried  thence  to  the  extreme  outer  edge 
of  the  main  plane,  back  to  the  tail,  and  from  this  to  a  loose  connec- 
tion, 60  feet  of  copper  wire  trailing  behind. 

Possible  Developments.  It  is  evident  that  these  isolated  experi- 
ments, while  more  or  less  numerous,  are  but  the  beginning  of  the 
serious  study  that  will  be  given  the  matter  within  the  next  year  or 
so.  Nine-hour,  non-stop  flights  covering  more  than  400  miles  give 
some  idea  of  what  will  be  accomplished  in  the  way  of  long-distance 
flying  in  the  near  future — in  fact,  they  make  the  possibility  of  being 
able  to  cover  more  than  1,000  miles  per  day  of  twenty-four  hours 
seem  very  close  at  hand,  so  that  Atwood's  proposal  to  fly  across  the 
Atlantic  in  three  days  appears  to  be  only  a  question  of  carrying  suf- 
ficient fuel.  To  be  able  to  keep  in  constant  communication  with 
these  long-distance  flyers  would  be  invaluable,  and  that  is  what 
experimenters  in  the  wireless  field  aim  to  accomplish. 

Wireless  telegraphy  from  the  dirigible  has  already  reached  a 


132 


WIRELESS   TELEGRAPHY  IN  AERONAUTICS       15 

more  advanced  stage,  as  neither  the  use  of  a  trailing  wire  nor  the 
matter  of  weight  present  such  serious  disadvantages  as  on  the  aero- 
plane. The  apparatus  used  on  the  British  military  dirigible  Beta 
weighed  approximately  100  pounds,  and  as  signals  have  been  sent 
50  miles  under  favorable  conditions,  the  proportions  of  weight  to 
distance  of  transmission  was,  roughly  speaking,  2  pounds.  But  an 
ordinary  induction  coil  and  accumulator  were  employed,  so  that 
this  can  scarcely  be  taken  as  a  criterion.  They  were  used  in  con- 
nection with  a  trailing  aerial  and  a  counter-capacity,  and,  as  the 
chief  requirement  of  the  latter  is  superficial  area  to  take  the  charge, 
as  light  a  substance  as  possible,  such  as  paper-thin  sheet  aluminum, 
could  be  employed. 

The  form  of  the  wireless  installation  suggested  by  one  of  the 
chief  English  experimenters  as  best  adapted  to  the  needs  of  the  air- 
ship, is  that  of  a  small  auxiliary  motor,  say,  a  two-cylinder,  3-  to  4- 
horse-power  machine,  directly  coupled  to  an  alternating  generator 
of  about  2  kilowatts  capacity,  together  with  an  aerial  about  350  feet 
long,  and  a  counter-capacity  in  the  form  of  very  thin  metallic  sheet- 
ing, suitably  disposed.  Considerable  attention  is  now  being  given 
to  the  production  of  portable  apparatus.  The  chief  limiting  factor 
in  connection  with  small  receivers  naturally  has  to  do  with  the 
detector,  the  vacuum  valve  type  of  Prof.  J.  A.  Fleming  probably 
being  the  most  suitable  in  many  respects,  and  next  to  that  an  elec- 
trolytic detector. 

Akron  Outfit.  The  ill-fated  dirigible  Akron,  in  which  Melvin 
Vaniman  had  intended  making  his  second  attempt  at  crossing  the 
Atlantic,  when  he  and  his  gallant  crew  were  killed  by  the  fall 
of  the  airship  due  to  the  explosion  of  the  gas  bag,  is  a  forcible 
example  of  the  careful  attention  now  being  given  to  wireless  equip- 
ment and  the  dependence  placed  upon  it  as  a  safeguard.  Vaniman 
was  particularly  fitted  by  experience  to  judge  of  the  wireless 
requirements  for  a  dirigible,  as,  it  will  be  recalled,  he  was  Wellman's 
chief  engineer  on  the  America,  and  he  had  taken  advantage  of  that 
experience  to  embody  all  the  improvements  in  the  new  equipment 
that  were  found  lacking  in  the  America's  set.  The  latter  had  a 
sending  range  of  only  80  to  90  miles,  so  that  while  the  operator 
could  catch  the  numerous  inquiries  that  filled  the  air  regarding  the 
America's  whereabouts  during  the  48  hours  or  more  that  it  was  out  of 


133 


16       WIRELESS   TELEGRAPHY  IN   AERONAUTICS 

sending  range,  he  could  not  reply  to  any  of  them.  The  equipment 
of  the  Akron  was  a  Marconi  set  with  a  sending  range  of  700  to  800 
miles  and  consisted  of  a  3-kilowatt,  120-cycle,  alternating-current 
generator,  direct  driven  by  a  17-horse-power,  4-cylinder  gasoline 
engine.  For  receiving,  the  most  advanced  type  of  musical,  rotary 
spark  gap  and  a  valve  detector  was  to  be  employed.  As  a  counter- 
capacity  does  not  permit  of  the  most  efficient  operation,  a  flexible, 
phosphor  bronze  wire  trailing  in  the  water  was  to  constitute  the 
ground,  the  equilibrator  which  was  used  for  that  purpose  on  the 
America  having  been  abandoned.  This  trailing  ground  was  wound 
on  a  drum  and  sufficient  wire  was  provided  to  reach  the  water  at  any 
point  from  100  to  1,200  feet  elevation,  the  amount  payed  out 
depending  upon  the  height  at  which  the  airship  was  flying.  How- 
ever, should  the  airship  rise  higher,  provision  had  been  made  to 
operate  the  equipment  as  an  unbalanced  Hertz  oscillator  without  a 
ground.  The  transmitter  was  of  the  loose-coupled  type  and  was  so 
arranged  that  considerable  variation  in  the  natural  period  of  the 
open  oscillating  circuit  would  have  a  minimum  effect  upon  the 
transmitted  signals.  The  frame  of  the  envelope  was  used  as  one  side 
of  the  oscillator,  the  trailing  ground  acting  as  the  other.  Particular 
care  had  been  taken  in  the  design  o!  the  various  parts  of  the  appa- 
ratus to  prevent  any  possibility  of  the  sparking,  or  high-tension 
discharge,  igniting  the  hydrogen  gas.  Jack  Irwin,  whose  call  of 
distress  from  the  America  brought  the  S.S.  Trent  to  their  rescue, 
was  to  have  accompanied  the  Akron  as  operator. 


134 


INDEX 


The  page  numbers  of  this  volume  will  be  found  at  the  bottom  of  the 
pages;  the  numbers  at  the  top  refer  only  to  the  section. 

A  Page 

Aerials 55 

Alternating-current  transformers 46 

B 

Bell's  photophone 91 

Bell's  radiophone 89 

Branly  coherer 24 

C 

Clark  system  of  radiotelegraphy 80 

Coherers 58 

Branly 58 

Italian  navy 59 

Lodge-Muirhead 58 

tantalum-mercury 59 

Collins  system  of  radiotelephony - 115 

Condensers 47 

D 

DeForest  system 

of  radiotelegraphy 79 

of  radiotelephony 113 

Detectors 57 

audion 62 

electrodynamic 65 

electrolytic 65 

Fessenden  liquid  barreter 65 

glow-lamp 61 

Hbzier-Brown 65 

magnetic 62 

thermo-electric 64 

valve,  or  rectifier 56 

E 

Electric  oscillations 12 

Electric  waves : 8 

Note. — For  page  numbers  sec  foot  of  pages. 


137 


2  INDEX 

Electric  waves  Page 

electric  oscillations 12 

electromagnetic  theory  of  light 8 

nature  of 11 

resonance 17 

wave-lengths 21 

work  of  Hertz 14 

Electromagnetic  medium 9 

Electromagnetic  theory  of  light 8 

electromagnetic  medium 9 

luminiferous  ether. .  9 


F 

Faraday,  work  of 10 

Fessenden  system 

of  radiotelegraphy 72 

of  radiotelephony 112 

H 

Hertz,  work  of 14 

energy  of  an  oscillator 16 

resonator 17 

High-frequency  alternators 52 

Hughes,  work  of 27 

I        «C' 

Induction  coils 41 

interrupters 42 

keys 45 

primary  condenser 42 

L 

Lodge,  work  of 27 

Lodge-Muirhead  system  of  radiotelegraphy 77 

Luminiferous  ether 9 


M 

Marconi,  work  of 27 

capacity  areas 31 

development  of  the  antennae , 31 

early  apparatus 28 

inductive  receiving  antennae 32 

inductive  transmitting  antennae 34 

Note. — For  page  numbers  see  foot  of  pages. 


138 


INDEX  3 

Marconi  system  Page 

of  radiotelegraphy 69 

of  radiotelephony 110 

Massie  system  of  radiotelegraphy 83 

Maxwell,  work  of 10 

O 

Oscillation  transformers 47 

P 

Poulsen  system 

of  radiotelegraphy 83 

of  radiotelephony 109 

R 

Radiotelegraphic  apparatus 40 

aerials 55 

alternating-current  transformers 46 

auxiliary  apparatus 66 

charging  devices 40 

condensers 47 

detectors 57 

directive  antennae 57 

high-frequency  alternators 52 

induction  coils 41 

measuring  instruments 67 

oscillation  transformers 47 

singing  arc 53 

sources  of  energy 40 

spark  gaps 49 

tuning  coils 49 

Radiotelegraphy 

development  of 23 

propagation  of  waves  from  grounded  oscillator 36 

selective  signaling 38 

systems  of 68 

Clark i 80 

DeForest 79 

Fessenden 72 

Lodge-Muirhead , 77 

Marconi 69 

Massie 83 

miscellaneous 83 

Poulsen 83 

Stone 82 

Telefunken 74 

Von  Lepel , 76 

Note. — For  page  numbers  see  foot  of  pages. 


139 


4  INDEX 

Page 

Radiotelephony,  systems  of 105 

Collins ; 115 

De  Forest 113 

Fessenden 112 

Marjorana 110 

Poulsen 109 

Ruhmer 108 

Telefunken 106 

Resonance 17 

Righi  oscillator 24 

Ruhmer  system  of  radiotelephony 108 


Singing  arc .  53 

Spark  gaps 49 

Stone  system  of  radiotelegraphy 82 

T 

Telefunken  system 

of  radiotelegraphy '. 74 

of  radiotelephony 106 

Telegraphic  codes 69 

Transformers 

alternating-current , 46 

oscillation 47 

Tuning  coils 49 


Von  Lepel  system  of  radiotelegraphy 76 

W 

Wave-lengths 21 

Wireless  telegraphy 1-86 

on  aeroplanes 

first  message 125 

general  problems '.  130 

Horton's  experiments • 126 

recent  records 127 

on  dirigibles 

early  experiments  on  balloons 119 

dangers  from  electric  discharge 120 

preventive  methods 122 

wireless  on  the  Zeppelins 124 

early  forms 2 

conduction  systems ; 2 

Morse  system 2 

Note. — For  page  numbers  see  foot  of  pages. 


140 


INDEX  5 

work  of  Steinhall 2 

induction  systems 4 

Dolbear  system 4 

Edison  system 5 

work  of  Preece 6 

electric  waves 8 

radiotelegraphy 

apparatus 40 

development  of 23 

systems  of 68 

Wireless  telephony  Page 

Bell's  photophone 91 

Bell's  radiophone 89 

"light  telephony" 91 

by  means  of  Hertzian  waves 92 

nature  of  a  high-frequency  telephone  current 94 

oscillation  generators 96 

receiving  arrangements 102 

selenium  cell 90 

systems  of  radio-telephony 105 

telephonic  control  of  oscillations 97 

transmitting  circuits 98 

two-way  transmission ...«..,.,  i .  t ......  104 

Note. — For  page  numbers  see  foot  of  pages. 


141 


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